diff --git a/build/Android.gtest.mk b/build/Android.gtest.mk
index af64470..d38cd63 100644
--- a/build/Android.gtest.mk
+++ b/build/Android.gtest.mk
@@ -39,6 +39,7 @@
   NonStaticLeafMethods \
   ProtoCompare \
   ProtoCompare2 \
+  ProfileTestMultiDex \
   StaticLeafMethods \
   Statics \
   StaticsFromCode \
@@ -65,7 +66,7 @@
 
 # Dex file dependencies for each gtest.
 ART_GTEST_class_linker_test_DEX_DEPS := Interfaces MultiDex MyClass Nested Statics StaticsFromCode
-ART_GTEST_compiler_driver_test_DEX_DEPS := AbstractMethod StaticLeafMethods
+ART_GTEST_compiler_driver_test_DEX_DEPS := AbstractMethod StaticLeafMethods ProfileTestMultiDex
 ART_GTEST_dex_cache_test_DEX_DEPS := Main
 ART_GTEST_dex_file_test_DEX_DEPS := GetMethodSignature Main Nested
 ART_GTEST_exception_test_DEX_DEPS := ExceptionHandle
@@ -78,6 +79,8 @@
 ART_GTEST_object_test_DEX_DEPS := ProtoCompare ProtoCompare2 StaticsFromCode XandY
 ART_GTEST_proxy_test_DEX_DEPS := Interfaces
 ART_GTEST_reflection_test_DEX_DEPS := Main NonStaticLeafMethods StaticLeafMethods
+ART_GTEST_profile_assistant_test_DEX_DEPS := ProfileTestMultiDex
+ART_GTEST_profile_compilation_info_test_DEX_DEPS := ProfileTestMultiDex
 ART_GTEST_stub_test_DEX_DEPS := AllFields
 ART_GTEST_transaction_test_DEX_DEPS := Transaction
 ART_GTEST_type_lookup_table_test_DEX_DEPS := Lookup
@@ -208,6 +211,7 @@
   runtime/interpreter/safe_math_test.cc \
   runtime/interpreter/unstarted_runtime_test.cc \
   runtime/java_vm_ext_test.cc \
+  runtime/jit/profile_compilation_info_test.cc \
   runtime/lambda/closure_test.cc \
   runtime/lambda/shorty_field_type_test.cc \
   runtime/leb128_test.cc \
@@ -267,6 +271,7 @@
   compiler/optimizing/ssa_test.cc \
   compiler/optimizing/stack_map_test.cc \
   compiler/optimizing/suspend_check_test.cc \
+  compiler/profile_assistant_test.cc \
   compiler/utils/arena_allocator_test.cc \
   compiler/utils/dedupe_set_test.cc \
   compiler/utils/swap_space_test.cc \
diff --git a/compiler/common_compiler_test.cc b/compiler/common_compiler_test.cc
index 9594dce..afc8463 100644
--- a/compiler/common_compiler_test.cc
+++ b/compiler/common_compiler_test.cc
@@ -168,6 +168,12 @@
   return nullptr;
 }
 
+// Get ProfileCompilationInfo that should be passed to the driver.
+ProfileCompilationInfo* CommonCompilerTest::GetProfileCompilationInfo() {
+  // Null, profile information will not be taken into account.
+  return nullptr;
+}
+
 void CommonCompilerTest::SetUp() {
   CommonRuntimeTest::SetUp();
   {
@@ -207,7 +213,7 @@
                                             timer_.get(),
                                             -1,
                                             /* dex_to_oat_map */ nullptr,
-                                            /* profile_compilation_info */ nullptr));
+                                            GetProfileCompilationInfo()));
   // We typically don't generate an image in unit tests, disable this optimization by default.
   compiler_driver_->SetSupportBootImageFixup(false);
 }
diff --git a/compiler/common_compiler_test.h b/compiler/common_compiler_test.h
index b491946..7e0fbab 100644
--- a/compiler/common_compiler_test.h
+++ b/compiler/common_compiler_test.h
@@ -23,6 +23,7 @@
 
 #include "common_runtime_test.h"
 #include "compiler.h"
+#include "jit/offline_profiling_info.h"
 #include "oat_file.h"
 
 namespace art {
@@ -75,6 +76,8 @@
   // driver assumes ownership of the set, so the test should properly release the set.
   virtual std::unordered_set<std::string>* GetCompiledMethods();
 
+  virtual ProfileCompilationInfo* GetProfileCompilationInfo();
+
   virtual void TearDown();
 
   void CompileClass(mirror::ClassLoader* class_loader, const char* class_name)
diff --git a/compiler/driver/compiler_driver_test.cc b/compiler/driver/compiler_driver_test.cc
index 82c0e86..4c03e5d 100644
--- a/compiler/driver/compiler_driver_test.cc
+++ b/compiler/driver/compiler_driver_test.cc
@@ -31,6 +31,7 @@
 #include "mirror/object_array-inl.h"
 #include "mirror/object-inl.h"
 #include "handle_scope-inl.h"
+#include "jit/offline_profiling_info.h"
 #include "scoped_thread_state_change.h"
 
 namespace art {
@@ -240,6 +241,94 @@
   EXPECT_TRUE(expected->empty());
 }
 
+class CompilerDriverProfileTest : public CompilerDriverTest {
+ protected:
+  ProfileCompilationInfo* GetProfileCompilationInfo() OVERRIDE {
+    ScopedObjectAccess soa(Thread::Current());
+    std::vector<std::unique_ptr<const DexFile>> dex_files = OpenTestDexFiles("ProfileTestMultiDex");
+
+    ProfileCompilationInfo info;
+    for (const std::unique_ptr<const DexFile>& dex_file : dex_files) {
+      std::cout << std::string(dex_file->GetLocation());
+      profile_info_.AddData(dex_file->GetLocation(), dex_file->GetLocationChecksum(), 1);
+      profile_info_.AddData(dex_file->GetLocation(), dex_file->GetLocationChecksum(), 2);
+    }
+    return &profile_info_;
+  }
+
+  std::unordered_set<std::string> GetExpectedMethodsForClass(const std::string& clazz) {
+    if (clazz == "Main") {
+      return std::unordered_set<std::string>({
+          "java.lang.String Main.getA()",
+          "java.lang.String Main.getB()"});
+    } else if (clazz == "Second") {
+      return std::unordered_set<std::string>({
+          "java.lang.String Second.getX()",
+          "java.lang.String Second.getY()"});
+    } else {
+      return std::unordered_set<std::string>();
+    }
+  }
+
+  void CheckCompiledMethods(jobject class_loader,
+                            const std::string& clazz,
+                            const std::unordered_set<std::string>& expected_methods) {
+    ClassLinker* class_linker = Runtime::Current()->GetClassLinker();
+    Thread* self = Thread::Current();
+    ScopedObjectAccess soa(self);
+    StackHandleScope<1> hs(self);
+    Handle<mirror::ClassLoader> h_loader(hs.NewHandle(
+        reinterpret_cast<mirror::ClassLoader*>(self->DecodeJObject(class_loader))));
+    mirror::Class* klass = class_linker->FindClass(self, clazz.c_str(), h_loader);
+    ASSERT_NE(klass, nullptr);
+
+    const auto pointer_size = class_linker->GetImagePointerSize();
+    size_t number_of_compiled_methods = 0;
+    for (auto& m : klass->GetVirtualMethods(pointer_size)) {
+      std::string name = PrettyMethod(&m, true);
+      const void* code = m.GetEntryPointFromQuickCompiledCodePtrSize(pointer_size);
+      ASSERT_NE(code, nullptr);
+      if (expected_methods.find(name) != expected_methods.end()) {
+        number_of_compiled_methods++;
+        EXPECT_FALSE(class_linker->IsQuickToInterpreterBridge(code));
+      } else {
+        EXPECT_TRUE(class_linker->IsQuickToInterpreterBridge(code));
+      }
+    }
+    EXPECT_EQ(expected_methods.size(), number_of_compiled_methods);
+  }
+
+ private:
+  ProfileCompilationInfo profile_info_;
+};
+
+TEST_F(CompilerDriverProfileTest, ProfileGuidedCompilation) {
+  TEST_DISABLED_FOR_HEAP_REFERENCE_POISONING_WITH_QUICK();
+  TEST_DISABLED_FOR_READ_BARRIER_WITH_QUICK();
+  TEST_DISABLED_FOR_READ_BARRIER_WITH_OPTIMIZING_FOR_UNSUPPORTED_INSTRUCTION_SETS();
+  Thread* self = Thread::Current();
+  jobject class_loader;
+  {
+    ScopedObjectAccess soa(self);
+    class_loader = LoadDex("ProfileTestMultiDex");
+  }
+  ASSERT_NE(class_loader, nullptr);
+
+  // Need to enable dex-file writability. Methods rejected to be compiled will run through the
+  // dex-to-dex compiler.
+  ProfileCompilationInfo info;
+  for (const DexFile* dex_file : GetDexFiles(class_loader)) {
+    ASSERT_TRUE(dex_file->EnableWrite());
+  }
+
+  CompileAll(class_loader);
+
+  std::unordered_set<std::string> m = GetExpectedMethodsForClass("Main");
+  std::unordered_set<std::string> s = GetExpectedMethodsForClass("Second");
+  CheckCompiledMethods(class_loader, "LMain;", m);
+  CheckCompiledMethods(class_loader, "LSecond;", s);
+}
+
 // TODO: need check-cast test (when stub complete & we can throw/catch
 
 }  // namespace art
diff --git a/compiler/profile_assistant.cc b/compiler/profile_assistant.cc
index 81f2a56..0871722 100644
--- a/compiler/profile_assistant.cc
+++ b/compiler/profile_assistant.cc
@@ -16,54 +16,150 @@
 
 #include "profile_assistant.h"
 
+#include "base/unix_file/fd_file.h"
+#include "os.h"
+
 namespace art {
 
 // Minimum number of new methods that profiles must contain to enable recompilation.
 static constexpr const uint32_t kMinNewMethodsForCompilation = 10;
 
-bool ProfileAssistant::ProcessProfiles(
-      const std::vector<std::string>& profile_files,
-      const std::vector<std::string>& reference_profile_files,
-      /*out*/ ProfileCompilationInfo** profile_compilation_info) {
+bool ProfileAssistant::ProcessProfilesInternal(
+        const std::vector<ScopedFlock>& profile_files,
+        const std::vector<ScopedFlock>& reference_profile_files,
+        /*out*/ ProfileCompilationInfo** profile_compilation_info) {
   DCHECK(!profile_files.empty());
-  DCHECK(reference_profile_files.empty() ||
+  DCHECK(!reference_profile_files.empty() ||
       (profile_files.size() == reference_profile_files.size()));
-
   std::vector<ProfileCompilationInfo> new_info(profile_files.size());
   bool should_compile = false;
   // Read the main profile files.
-  for (size_t i = 0; i < profile_files.size(); i++) {
-    if (!new_info[i].Load(profile_files[i])) {
-      LOG(WARNING) << "Could not load profile file: " << profile_files[i];
+  for (size_t i = 0; i < new_info.size(); i++) {
+    if (!new_info[i].Load(profile_files[i].GetFile()->Fd())) {
+      LOG(WARNING) << "Could not load profile file at index " << i;
       return false;
     }
     // Do we have enough new profiled methods that will make the compilation worthwhile?
     should_compile |= (new_info[i].GetNumberOfMethods() > kMinNewMethodsForCompilation);
   }
+
   if (!should_compile) {
     *profile_compilation_info = nullptr;
     return true;
   }
 
   std::unique_ptr<ProfileCompilationInfo> result(new ProfileCompilationInfo());
+  // Merge information.
   for (size_t i = 0; i < new_info.size(); i++) {
-    // Merge all data into a single object.
-    result->Load(new_info[i]);
-    // If we have any reference profile information merge their information with
-    // the current profiles and save them back to disk.
     if (!reference_profile_files.empty()) {
-      if (!new_info[i].Load(reference_profile_files[i])) {
-        LOG(WARNING) << "Could not load reference profile file: " << reference_profile_files[i];
+      if (!new_info[i].Load(reference_profile_files[i].GetFile()->Fd())) {
+        LOG(WARNING) << "Could not load reference profile file at index " << i;
         return false;
       }
-      if (!new_info[i].Save(reference_profile_files[i])) {
-        LOG(WARNING) << "Could not save reference profile file: " << reference_profile_files[i];
+    }
+    // Merge all data into a single object.
+    if (!result->Load(new_info[i])) {
+      LOG(WARNING) << "Could not merge profile data at index " << i;
+      return false;
+    }
+  }
+  // We were successful in merging all profile information. Update the files.
+  for (size_t i = 0; i < new_info.size(); i++) {
+    if (!reference_profile_files.empty()) {
+      if (!reference_profile_files[i].GetFile()->ClearContent()) {
+        PLOG(WARNING) << "Could not clear reference profile file at index " << i;
+        return false;
+      }
+      if (!new_info[i].Save(reference_profile_files[i].GetFile()->Fd())) {
+        LOG(WARNING) << "Could not save reference profile file at index " << i;
+        return false;
+      }
+      if (!profile_files[i].GetFile()->ClearContent()) {
+        PLOG(WARNING) << "Could not clear profile file at index " << i;
         return false;
       }
     }
   }
+
   *profile_compilation_info = result.release();
   return true;
 }
 
+class ScopedCollectionFlock {
+ public:
+  explicit ScopedCollectionFlock(size_t size) : flocks_(size) {}
+
+  // Will block until all the locks are acquired.
+  bool Init(const std::vector<std::string>& filenames, /* out */ std::string* error) {
+    for (size_t i = 0; i < filenames.size(); i++) {
+      if (!flocks_[i].Init(filenames[i].c_str(), O_RDWR, /* block */ true, error)) {
+        *error += " (index=" + std::to_string(i) + ")";
+        return false;
+      }
+    }
+    return true;
+  }
+
+  // Will block until all the locks are acquired.
+  bool Init(const std::vector<uint32_t>& fds, /* out */ std::string* error) {
+    for (size_t i = 0; i < fds.size(); i++) {
+      // We do not own the descriptor, so disable auto-close and don't check usage.
+      File file(fds[i], false);
+      file.DisableAutoClose();
+      if (!flocks_[i].Init(&file, error)) {
+        *error += " (index=" + std::to_string(i) + ")";
+        return false;
+      }
+    }
+    return true;
+  }
+
+  const std::vector<ScopedFlock>& Get() const { return flocks_; }
+
+ private:
+  std::vector<ScopedFlock> flocks_;
+};
+
+bool ProfileAssistant::ProcessProfiles(
+        const std::vector<uint32_t>& profile_files_fd,
+        const std::vector<uint32_t>& reference_profile_files_fd,
+        /*out*/ ProfileCompilationInfo** profile_compilation_info) {
+  std::string error;
+  ScopedCollectionFlock profile_files_flocks(profile_files_fd.size());
+  if (!profile_files_flocks.Init(profile_files_fd, &error)) {
+    LOG(WARNING) << "Could not lock profile files: " << error;
+    return false;
+  }
+  ScopedCollectionFlock reference_profile_files_flocks(reference_profile_files_fd.size());
+  if (!reference_profile_files_flocks.Init(reference_profile_files_fd, &error)) {
+    LOG(WARNING) << "Could not lock reference profile files: " << error;
+    return false;
+  }
+
+  return ProcessProfilesInternal(profile_files_flocks.Get(),
+                                 reference_profile_files_flocks.Get(),
+                                 profile_compilation_info);
+}
+
+bool ProfileAssistant::ProcessProfiles(
+        const std::vector<std::string>& profile_files,
+        const std::vector<std::string>& reference_profile_files,
+        /*out*/ ProfileCompilationInfo** profile_compilation_info) {
+  std::string error;
+  ScopedCollectionFlock profile_files_flocks(profile_files.size());
+  if (!profile_files_flocks.Init(profile_files, &error)) {
+    LOG(WARNING) << "Could not lock profile files: " << error;
+    return false;
+  }
+  ScopedCollectionFlock reference_profile_files_flocks(reference_profile_files.size());
+  if (!reference_profile_files_flocks.Init(reference_profile_files, &error)) {
+    LOG(WARNING) << "Could not lock reference profile files: " << error;
+    return false;
+  }
+
+  return ProcessProfilesInternal(profile_files_flocks.Get(),
+                                 reference_profile_files_flocks.Get(),
+                                 profile_compilation_info);
+}
+
 }  // namespace art
diff --git a/compiler/profile_assistant.h b/compiler/profile_assistant.h
index 088c8bd..ad5e216 100644
--- a/compiler/profile_assistant.h
+++ b/compiler/profile_assistant.h
@@ -20,6 +20,7 @@
 #include <string>
 #include <vector>
 
+#include "base/scoped_flock.h"
 #include "jit/offline_profiling_info.cc"
 
 namespace art {
@@ -52,7 +53,17 @@
       const std::vector<std::string>& reference_profile_files,
       /*out*/ ProfileCompilationInfo** profile_compilation_info);
 
+  static bool ProcessProfiles(
+      const std::vector<uint32_t>& profile_files_fd_,
+      const std::vector<uint32_t>& reference_profile_files_fd_,
+      /*out*/ ProfileCompilationInfo** profile_compilation_info);
+
  private:
+  static bool ProcessProfilesInternal(
+      const std::vector<ScopedFlock>& profile_files,
+      const std::vector<ScopedFlock>& reference_profile_files,
+      /*out*/ ProfileCompilationInfo** profile_compilation_info);
+
   DISALLOW_COPY_AND_ASSIGN(ProfileAssistant);
 };
 
diff --git a/compiler/profile_assistant_test.cc b/compiler/profile_assistant_test.cc
new file mode 100644
index 0000000..cecb865
--- /dev/null
+++ b/compiler/profile_assistant_test.cc
@@ -0,0 +1,279 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <gtest/gtest.h>
+
+#include "base/unix_file/fd_file.h"
+#include "common_runtime_test.h"
+#include "compiler/profile_assistant.h"
+#include "jit/offline_profiling_info.h"
+
+namespace art {
+
+class ProfileAssistantTest : public CommonRuntimeTest {
+ protected:
+  void SetupProfile(const std::string& id,
+                    uint32_t checksum,
+                    uint16_t number_of_methods,
+                    const ScratchFile& profile,
+                    ProfileCompilationInfo* info,
+                    uint16_t start_method_index = 0) {
+    std::string dex_location1 = "location1" + id;
+    uint32_t dex_location_checksum1 = checksum;
+    std::string dex_location2 = "location2" + id;
+    uint32_t dex_location_checksum2 = 10 * checksum;
+    for (uint16_t i = start_method_index; i < start_method_index + number_of_methods; i++) {
+      ASSERT_TRUE(info->AddData(dex_location1, dex_location_checksum1, i));
+      ASSERT_TRUE(info->AddData(dex_location2, dex_location_checksum2, i));
+    }
+    ASSERT_TRUE(info->Save(GetFd(profile)));
+    ASSERT_EQ(0, profile.GetFile()->Flush());
+    ASSERT_TRUE(profile.GetFile()->ResetOffset());
+  }
+
+  uint32_t GetFd(const ScratchFile& file) const {
+    return static_cast<uint32_t>(file.GetFd());
+  }
+};
+
+TEST_F(ProfileAssistantTest, AdviseCompilationEmptyReferences) {
+  ScratchFile profile1;
+  ScratchFile profile2;
+  ScratchFile reference_profile1;
+  ScratchFile reference_profile2;
+
+  std::vector<uint32_t> profile_fds({
+      GetFd(profile1),
+      GetFd(profile2)});
+  std::vector<uint32_t> reference_profile_fds({
+      GetFd(reference_profile1),
+      GetFd(reference_profile2)});
+
+  const uint16_t kNumberOfMethodsToEnableCompilation = 100;
+  ProfileCompilationInfo info1;
+  SetupProfile("p1", 1, kNumberOfMethodsToEnableCompilation, profile1, &info1);
+  ProfileCompilationInfo info2;
+  SetupProfile("p2", 2, kNumberOfMethodsToEnableCompilation, profile2, &info2);
+
+  // We should advise compilation.
+  ProfileCompilationInfo* result;
+  ASSERT_TRUE(ProfileAssistant::ProcessProfiles(profile_fds, reference_profile_fds, &result));
+  ASSERT_TRUE(result != nullptr);
+
+  // The resulting compilation info must be equal to the merge of the inputs.
+  ProfileCompilationInfo expected;
+  ASSERT_TRUE(expected.Load(info1));
+  ASSERT_TRUE(expected.Load(info2));
+  ASSERT_TRUE(expected.Equals(*result));
+
+  // The information from profiles must be transfered to the reference profiles.
+  ProfileCompilationInfo file_info1;
+  ASSERT_TRUE(reference_profile1.GetFile()->ResetOffset());
+  ASSERT_TRUE(file_info1.Load(GetFd(reference_profile1)));
+  ASSERT_TRUE(file_info1.Equals(info1));
+
+  ProfileCompilationInfo file_info2;
+  ASSERT_TRUE(reference_profile2.GetFile()->ResetOffset());
+  ASSERT_TRUE(file_info2.Load(GetFd(reference_profile2)));
+  ASSERT_TRUE(file_info2.Equals(info2));
+
+  // Initial profiles must be cleared.
+  ASSERT_EQ(0, profile1.GetFile()->GetLength());
+  ASSERT_EQ(0, profile2.GetFile()->GetLength());
+}
+
+TEST_F(ProfileAssistantTest, AdviseCompilationNonEmptyReferences) {
+  ScratchFile profile1;
+  ScratchFile profile2;
+  ScratchFile reference_profile1;
+  ScratchFile reference_profile2;
+
+  std::vector<uint32_t> profile_fds({
+      GetFd(profile1),
+      GetFd(profile2)});
+  std::vector<uint32_t> reference_profile_fds({
+      GetFd(reference_profile1),
+      GetFd(reference_profile2)});
+
+  // The new profile info will contain the methods with indices 0-100.
+  const uint16_t kNumberOfMethodsToEnableCompilation = 100;
+  ProfileCompilationInfo info1;
+  SetupProfile("p1", 1, kNumberOfMethodsToEnableCompilation, profile1, &info1);
+  ProfileCompilationInfo info2;
+  SetupProfile("p2", 2, kNumberOfMethodsToEnableCompilation, profile2, &info2);
+
+
+  // The reference profile info will contain the methods with indices 50-150.
+  const uint16_t kNumberOfMethodsAlreadyCompiled = 100;
+  ProfileCompilationInfo reference_info1;
+  SetupProfile("p1", 1, kNumberOfMethodsAlreadyCompiled, reference_profile1,
+      &reference_info1, kNumberOfMethodsToEnableCompilation / 2);
+  ProfileCompilationInfo reference_info2;
+  SetupProfile("p2", 2, kNumberOfMethodsAlreadyCompiled, reference_profile2,
+      &reference_info2, kNumberOfMethodsToEnableCompilation / 2);
+
+  // We should advise compilation.
+  ProfileCompilationInfo* result;
+  ASSERT_TRUE(ProfileAssistant::ProcessProfiles(profile_fds, reference_profile_fds, &result));
+  ASSERT_TRUE(result != nullptr);
+
+  // The resulting compilation info must be equal to the merge of the inputs
+  ProfileCompilationInfo expected;
+  ASSERT_TRUE(expected.Load(info1));
+  ASSERT_TRUE(expected.Load(info2));
+  ASSERT_TRUE(expected.Load(reference_info1));
+  ASSERT_TRUE(expected.Load(reference_info2));
+  ASSERT_TRUE(expected.Equals(*result));
+
+  // The information from profiles must be transfered to the reference profiles.
+  ProfileCompilationInfo file_info1;
+  ProfileCompilationInfo merge1;
+  ASSERT_TRUE(merge1.Load(info1));
+  ASSERT_TRUE(merge1.Load(reference_info1));
+  ASSERT_TRUE(reference_profile1.GetFile()->ResetOffset());
+  ASSERT_TRUE(file_info1.Load(GetFd(reference_profile1)));
+  ASSERT_TRUE(file_info1.Equals(merge1));
+
+  ProfileCompilationInfo file_info2;
+  ProfileCompilationInfo merge2;
+  ASSERT_TRUE(merge2.Load(info2));
+  ASSERT_TRUE(merge2.Load(reference_info2));
+  ASSERT_TRUE(reference_profile2.GetFile()->ResetOffset());
+  ASSERT_TRUE(file_info2.Load(GetFd(reference_profile2)));
+  ASSERT_TRUE(file_info2.Equals(merge2));
+
+  // Initial profiles must be cleared.
+  ASSERT_EQ(0, profile1.GetFile()->GetLength());
+  ASSERT_EQ(0, profile2.GetFile()->GetLength());
+}
+
+TEST_F(ProfileAssistantTest, DoNotAdviseCompilation) {
+  ScratchFile profile1;
+  ScratchFile profile2;
+  ScratchFile reference_profile1;
+  ScratchFile reference_profile2;
+
+  std::vector<uint32_t> profile_fds({
+      GetFd(profile1),
+      GetFd(profile2)});
+  std::vector<uint32_t> reference_profile_fds({
+      GetFd(reference_profile1),
+      GetFd(reference_profile2)});
+
+  const uint16_t kNumberOfMethodsToSkipCompilation = 1;
+  ProfileCompilationInfo info1;
+  SetupProfile("p1", 1, kNumberOfMethodsToSkipCompilation, profile1, &info1);
+  ProfileCompilationInfo info2;
+  SetupProfile("p2", 2, kNumberOfMethodsToSkipCompilation, profile2, &info2);
+
+  // We should not advise compilation.
+  ProfileCompilationInfo* result;
+  ASSERT_TRUE(ProfileAssistant::ProcessProfiles(profile_fds, reference_profile_fds, &result));
+  ASSERT_TRUE(result == nullptr);
+
+  // The information from profiles must remain the same.
+  ProfileCompilationInfo file_info1;
+  ASSERT_TRUE(profile1.GetFile()->ResetOffset());
+  ASSERT_TRUE(file_info1.Load(GetFd(profile1)));
+  ASSERT_TRUE(file_info1.Equals(info1));
+
+  ProfileCompilationInfo file_info2;
+  ASSERT_TRUE(profile2.GetFile()->ResetOffset());
+  ASSERT_TRUE(file_info2.Load(GetFd(profile2)));
+  ASSERT_TRUE(file_info2.Equals(info2));
+
+  // Reference profile files must remain empty.
+  ASSERT_EQ(0, reference_profile1.GetFile()->GetLength());
+  ASSERT_EQ(0, reference_profile2.GetFile()->GetLength());
+}
+
+TEST_F(ProfileAssistantTest, FailProcessingBecauseOfProfiles) {
+  ScratchFile profile1;
+  ScratchFile profile2;
+  ScratchFile reference_profile1;
+  ScratchFile reference_profile2;
+
+  std::vector<uint32_t> profile_fds({
+      GetFd(profile1),
+      GetFd(profile2)});
+  std::vector<uint32_t> reference_profile_fds({
+      GetFd(reference_profile1),
+      GetFd(reference_profile2)});
+
+  const uint16_t kNumberOfMethodsToEnableCompilation = 100;
+  // Assign different hashes for the same dex file. This will make merging of information to fail.
+  ProfileCompilationInfo info1;
+  SetupProfile("p1", 1, kNumberOfMethodsToEnableCompilation, profile1, &info1);
+  ProfileCompilationInfo info2;
+  SetupProfile("p1", 2, kNumberOfMethodsToEnableCompilation, profile2, &info2);
+
+  // We should fail processing.
+  ProfileCompilationInfo* result;
+  ASSERT_FALSE(ProfileAssistant::ProcessProfiles(profile_fds, reference_profile_fds, &result));
+  ASSERT_TRUE(result == nullptr);
+
+  // The information from profiles must still remain the same.
+  ProfileCompilationInfo file_info1;
+  ASSERT_TRUE(profile1.GetFile()->ResetOffset());
+  ASSERT_TRUE(file_info1.Load(GetFd(profile1)));
+  ASSERT_TRUE(file_info1.Equals(info1));
+
+  ProfileCompilationInfo file_info2;
+  ASSERT_TRUE(profile2.GetFile()->ResetOffset());
+  ASSERT_TRUE(file_info2.Load(GetFd(profile2)));
+  ASSERT_TRUE(file_info2.Equals(info2));
+
+  // Reference profile files must still remain empty.
+  ASSERT_EQ(0, reference_profile1.GetFile()->GetLength());
+  ASSERT_EQ(0, reference_profile2.GetFile()->GetLength());
+}
+
+TEST_F(ProfileAssistantTest, FailProcessingBecauseOfReferenceProfiles) {
+  ScratchFile profile1;
+  ScratchFile reference_profile;
+
+  std::vector<uint32_t> profile_fds({
+      GetFd(profile1)});
+  std::vector<uint32_t> reference_profile_fds({
+      GetFd(reference_profile)});
+
+  const uint16_t kNumberOfMethodsToEnableCompilation = 100;
+  // Assign different hashes for the same dex file. This will make merging of information to fail.
+  ProfileCompilationInfo info1;
+  SetupProfile("p1", 1, kNumberOfMethodsToEnableCompilation, profile1, &info1);
+  ProfileCompilationInfo reference_info;
+  SetupProfile("p1", 2, kNumberOfMethodsToEnableCompilation, reference_profile, &reference_info);
+
+  // We should not advise compilation.
+  ProfileCompilationInfo* result;
+  ASSERT_TRUE(profile1.GetFile()->ResetOffset());
+  ASSERT_TRUE(reference_profile.GetFile()->ResetOffset());
+  ASSERT_FALSE(ProfileAssistant::ProcessProfiles(profile_fds, reference_profile_fds, &result));
+  ASSERT_TRUE(result == nullptr);
+
+  // The information from profiles must still remain the same.
+  ProfileCompilationInfo file_info1;
+  ASSERT_TRUE(profile1.GetFile()->ResetOffset());
+  ASSERT_TRUE(file_info1.Load(GetFd(profile1)));
+  ASSERT_TRUE(file_info1.Equals(info1));
+
+  ProfileCompilationInfo file_info2;
+  ASSERT_TRUE(reference_profile.GetFile()->ResetOffset());
+  ASSERT_TRUE(file_info2.Load(GetFd(reference_profile)));
+  ASSERT_TRUE(file_info2.Equals(reference_info));
+}
+
+}  // namespace art
diff --git a/dex2oat/dex2oat.cc b/dex2oat/dex2oat.cc
index dbb7341..52c2283 100644
--- a/dex2oat/dex2oat.cc
+++ b/dex2oat/dex2oat.cc
@@ -340,6 +340,12 @@
   UsageError("      --profile-file will be merged into --reference-profile-file. Valid only when");
   UsageError("      specified together with --profile-file.");
   UsageError("");
+  UsageError("  --profile-file-fd=<number>: same as --profile-file but accepts a file descriptor.");
+  UsageError("      Cannot be used together with --profile-file.");
+  UsageError("");
+  UsageError("  --reference-profile-file-fd=<number>: same as --reference-profile-file but");
+  UsageError("      accepts a file descriptor. Cannot be used together with");
+  UsageError("       --reference-profile-file.");
   UsageError("  --print-pass-names: print a list of pass names");
   UsageError("");
   UsageError("  --disable-passes=<pass-names>:  disable one or more passes separated by comma.");
@@ -497,6 +503,14 @@
   return dex_files_size >= kMinDexFileCumulativeSizeForSwap;
 }
 
+static void CloseAllFds(const std::vector<uint32_t>& fds, const char* descriptor) {
+  for (size_t i = 0; i < fds.size(); i++) {
+    if (close(fds[i]) < 0) {
+      PLOG(WARNING) << "Failed to close descriptor for " << descriptor << " at index " << i;
+    }
+  }
+}
+
 class Dex2Oat FINAL {
  public:
   explicit Dex2Oat(TimingLogger* timings) :
@@ -575,6 +589,14 @@
     ParseUintOption(option, "--oat-fd", &oat_fd_, Usage);
   }
 
+  void ParseFdForCollection(const StringPiece& option,
+                            const char* arg_name,
+                            std::vector<uint32_t>* fds) {
+    uint32_t fd;
+    ParseUintOption(option, arg_name, &fd, Usage);
+    fds->push_back(fd);
+  }
+
   void ParseJ(const StringPiece& option) {
     ParseUintOption(option, "-j", &thread_count_, Usage, /* is_long_option */ false);
   }
@@ -778,11 +800,25 @@
       }
     }
 
+    if (!profile_files_.empty() && !profile_files_fd_.empty()) {
+      Usage("Profile files should not be specified with both --profile-file-fd and --profile-file");
+    }
     if (!profile_files_.empty()) {
       if (!reference_profile_files_.empty() &&
           (reference_profile_files_.size() != profile_files_.size())) {
         Usage("If specified, --reference-profile-file should match the number of --profile-file.");
       }
+    } else if (!reference_profile_files_.empty()) {
+      Usage("--reference-profile-file should only be supplied with --profile-file");
+    }
+    if (!profile_files_fd_.empty()) {
+      if (!reference_profile_files_fd_.empty() &&
+          (reference_profile_files_fd_.size() != profile_files_fd_.size())) {
+        Usage("If specified, --reference-profile-file-fd should match the number",
+              " of --profile-file-fd.");
+      }
+    } else if (!reference_profile_files_fd_.empty()) {
+      Usage("--reference-profile-file-fd should only be supplied with --profile-file-fd");
     }
 
     if (!parser_options->oat_symbols.empty()) {
@@ -1076,6 +1112,10 @@
       } else if (option.starts_with("--reference-profile-file=")) {
         reference_profile_files_.push_back(
             option.substr(strlen("--reference-profile-file=")).ToString());
+      } else if (option.starts_with("--profile-file-fd=")) {
+        ParseFdForCollection(option, "--profile-file-fd", &profile_files_fd_);
+      } else if (option.starts_with("--reference-profile-file-fd=")) {
+        ParseFdForCollection(option, "--reference_profile-file-fd", &reference_profile_files_fd_);
       } else if (option == "--no-profile-file") {
         // No profile
       } else if (option == "--host") {
@@ -1815,17 +1855,27 @@
   }
 
   bool UseProfileGuidedCompilation() const {
-    return !profile_files_.empty();
+    return !profile_files_.empty() || !profile_files_fd_.empty();
   }
 
   bool ProcessProfiles() {
     DCHECK(UseProfileGuidedCompilation());
     ProfileCompilationInfo* info = nullptr;
-    if (ProfileAssistant::ProcessProfiles(profile_files_, reference_profile_files_, &info)) {
-      profile_compilation_info_.reset(info);
-      return true;
+    bool result = false;
+    if (profile_files_.empty()) {
+      DCHECK(!profile_files_fd_.empty());
+      result = ProfileAssistant::ProcessProfiles(
+          profile_files_fd_, reference_profile_files_fd_, &info);
+      CloseAllFds(profile_files_fd_, "profile_files_fd_");
+      CloseAllFds(reference_profile_files_fd_, "reference_profile_files_fd_");
+    } else {
+      result = ProfileAssistant::ProcessProfiles(
+          profile_files_, reference_profile_files_, &info);
     }
-    return false;
+
+    profile_compilation_info_.reset(info);
+
+    return result;
   }
 
   bool ShouldCompileBasedOnProfiles() const {
@@ -2311,6 +2361,8 @@
   int app_image_fd_;
   std::vector<std::string> profile_files_;
   std::vector<std::string> reference_profile_files_;
+  std::vector<uint32_t> profile_files_fd_;
+  std::vector<uint32_t> reference_profile_files_fd_;
   std::unique_ptr<ProfileCompilationInfo> profile_compilation_info_;
   TimingLogger* timings_;
   std::unique_ptr<CumulativeLogger> compiler_phases_timings_;
diff --git a/runtime/base/scoped_flock.cc b/runtime/base/scoped_flock.cc
index 71e0590..814cbd0 100644
--- a/runtime/base/scoped_flock.cc
+++ b/runtime/base/scoped_flock.cc
@@ -26,16 +26,25 @@
 namespace art {
 
 bool ScopedFlock::Init(const char* filename, std::string* error_msg) {
+  return Init(filename, O_CREAT | O_RDWR, true, error_msg);
+}
+
+bool ScopedFlock::Init(const char* filename, int flags, bool block, std::string* error_msg) {
   while (true) {
     if (file_.get() != nullptr) {
       UNUSED(file_->FlushCloseOrErase());  // Ignore result.
     }
-    file_.reset(OS::OpenFileWithFlags(filename, O_CREAT | O_RDWR));
+    file_.reset(OS::OpenFileWithFlags(filename, flags));
     if (file_.get() == nullptr) {
       *error_msg = StringPrintf("Failed to open file '%s': %s", filename, strerror(errno));
       return false;
     }
-    int flock_result = TEMP_FAILURE_RETRY(flock(file_->Fd(), LOCK_EX));
+    int operation = block ? LOCK_EX : (LOCK_EX | LOCK_NB);
+    int flock_result = TEMP_FAILURE_RETRY(flock(file_->Fd(), operation));
+    if (flock_result == EWOULDBLOCK) {
+      // File is locked by someone else and we are required not to block;
+      return false;
+    }
     if (flock_result != 0) {
       *error_msg = StringPrintf("Failed to lock file '%s': %s", filename, strerror(errno));
       return false;
@@ -51,11 +60,23 @@
     if (stat_result != 0) {
       PLOG(WARNING) << "Failed to stat, will retry: " << filename;
       // ENOENT can happen if someone racing with us unlinks the file we created so just retry.
-      continue;
+      if (block) {
+        continue;
+      } else {
+        // Note that in theory we could race with someone here for a long time and end up retrying
+        // over and over again. This potential behavior does not fit well in the non-blocking
+        // semantics. Thus, if we are not require to block return failure when racing.
+        return false;
+      }
     }
     if (fstat_stat.st_dev != stat_stat.st_dev || fstat_stat.st_ino != stat_stat.st_ino) {
       LOG(WARNING) << "File changed while locking, will retry: " << filename;
-      continue;
+      if (block) {
+        continue;
+      } else {
+        // See comment above.
+        return false;
+      }
     }
     return true;
   }
@@ -78,7 +99,7 @@
   return true;
 }
 
-File* ScopedFlock::GetFile() {
+File* ScopedFlock::GetFile() const {
   CHECK(file_.get() != nullptr);
   return file_.get();
 }
diff --git a/runtime/base/scoped_flock.h b/runtime/base/scoped_flock.h
index 08612e3..cc22056 100644
--- a/runtime/base/scoped_flock.h
+++ b/runtime/base/scoped_flock.h
@@ -32,10 +32,15 @@
   // Attempts to acquire an exclusive file lock (see flock(2)) on the file
   // at filename, and blocks until it can do so.
   //
-  // Returns true if the lock could be acquired, or false if an error
-  // occurred. It is an error if the file does not exist, or if its inode
-  // changed (usually due to a new file being created at the same path)
-  // between attempts to lock it.
+  // Returns true if the lock could be acquired, or false if an error occurred.
+  // It is an error if its inode changed (usually due to a new file being
+  // created at the same path) between attempts to lock it. In blocking mode,
+  // locking will be retried if the file changed. In non-blocking mode, false
+  // is returned and no attempt is made to re-acquire the lock.
+  //
+  // The file is opened with the provided flags.
+  bool Init(const char* filename, int flags, bool block, std::string* error_msg);
+  // Calls Init(filename, O_CREAT | O_RDWR, true, errror_msg)
   bool Init(const char* filename, std::string* error_msg);
   // Attempt to acquire an exclusive file lock (see flock(2)) on 'file'.
   // Returns true if the lock could be acquired or false if an error
@@ -43,7 +48,7 @@
   bool Init(File* file, std::string* error_msg);
 
   // Returns the (locked) file associated with this instance.
-  File* GetFile();
+  File* GetFile() const;
 
   // Returns whether a file is held.
   bool HasFile();
diff --git a/runtime/base/unix_file/fd_file.cc b/runtime/base/unix_file/fd_file.cc
index 78bc3d5..e17bebb 100644
--- a/runtime/base/unix_file/fd_file.cc
+++ b/runtime/base/unix_file/fd_file.cc
@@ -316,4 +316,21 @@
   guard_state_ = GuardState::kNoCheck;
 }
 
+bool FdFile::ClearContent() {
+  if (SetLength(0) < 0) {
+    PLOG(art::ERROR) << "Failed to reset the length";
+    return false;
+  }
+  return ResetOffset();
+}
+
+bool FdFile::ResetOffset() {
+  off_t rc =  TEMP_FAILURE_RETRY(lseek(fd_, 0, SEEK_SET));
+  if (rc == static_cast<off_t>(-1)) {
+    PLOG(art::ERROR) << "Failed to reset the offset";
+    return false;
+  }
+  return true;
+}
+
 }  // namespace unix_file
diff --git a/runtime/base/unix_file/fd_file.h b/runtime/base/unix_file/fd_file.h
index 231a1ab..1e2d8af 100644
--- a/runtime/base/unix_file/fd_file.h
+++ b/runtime/base/unix_file/fd_file.h
@@ -79,6 +79,11 @@
 
   // Copy data from another file.
   bool Copy(FdFile* input_file, int64_t offset, int64_t size);
+  // Clears the file content and resets the file offset to 0.
+  // Returns true upon success, false otherwise.
+  bool ClearContent();
+  // Resets the file offset to the beginning of the file.
+  bool ResetOffset();
 
   // This enum is public so that we can define the << operator over it.
   enum class GuardState {
diff --git a/runtime/jit/offline_profiling_info.cc b/runtime/jit/offline_profiling_info.cc
index a132701..b4b872f 100644
--- a/runtime/jit/offline_profiling_info.cc
+++ b/runtime/jit/offline_profiling_info.cc
@@ -24,8 +24,11 @@
 
 #include "art_method-inl.h"
 #include "base/mutex.h"
+#include "base/scoped_flock.h"
 #include "base/stl_util.h"
+#include "base/unix_file/fd_file.h"
 #include "jit/profiling_info.h"
+#include "os.h"
 #include "safe_map.h"
 
 namespace art {
@@ -37,8 +40,17 @@
     return true;
   }
 
+  ScopedFlock flock;
+  std::string error;
+  if (!flock.Init(filename.c_str(), O_RDWR | O_NOFOLLOW | O_CLOEXEC, /* block */ false, &error)) {
+    LOG(WARNING) << "Couldn't lock the profile file " << filename << ": " << error;
+    return false;
+  }
+
+  int fd = flock.GetFile()->Fd();
+
   ProfileCompilationInfo info;
-  if (!info.Load(filename)) {
+  if (!info.Load(fd)) {
     LOG(WARNING) << "Could not load previous profile data from file " << filename;
     return false;
   }
@@ -54,9 +66,14 @@
     }
   }
 
+  if (!flock.GetFile()->ClearContent()) {
+    PLOG(WARNING) << "Could not clear profile file: " << filename;
+    return false;
+  }
+
   // This doesn't need locking because we are trying to lock the file for exclusive
   // access and fail immediately if we can't.
-  bool result = info.Save(filename);
+  bool result = info.Save(fd);
   if (result) {
     VLOG(profiler) << "Successfully saved profile info to " << filename
         << " Size: " << GetFileSizeBytes(filename);
@@ -66,64 +83,20 @@
   return result;
 }
 
-enum OpenMode {
-  READ,
-  READ_WRITE
-};
-
-static int OpenFile(const std::string& filename, OpenMode open_mode) {
-  int fd = -1;
-  switch (open_mode) {
-    case READ:
-      fd = open(filename.c_str(), O_RDONLY);
-      break;
-    case READ_WRITE:
-      // TODO(calin) allow the shared uid of the app to access the file.
-      fd = open(filename.c_str(), O_WRONLY | O_TRUNC | O_NOFOLLOW | O_CLOEXEC);
-      break;
-  }
-
-  if (fd < 0) {
-    PLOG(WARNING) << "Failed to open profile file " << filename;
-    return -1;
-  }
-
-  // Lock the file for exclusive access but don't wait if we can't lock it.
-  int err = flock(fd, LOCK_EX | LOCK_NB);
-  if (err < 0) {
-    PLOG(WARNING) << "Failed to lock profile file " << filename;
-    return -1;
-  }
-  return fd;
-}
-
-static bool CloseDescriptorForFile(int fd, const std::string& filename) {
-  // Now unlock the file, allowing another process in.
-  int err = flock(fd, LOCK_UN);
-  if (err < 0) {
-    PLOG(WARNING) << "Failed to unlock profile file " << filename;
-    return false;
-  }
-
-  // Done, close the file.
-  err = ::close(fd);
-  if (err < 0) {
-    PLOG(WARNING) << "Failed to close descriptor for profile file" << filename;
-    return false;
-  }
-
-  return true;
-}
-
-static void WriteToFile(int fd, const std::ostringstream& os) {
+static bool WriteToFile(int fd, const std::ostringstream& os) {
   std::string data(os.str());
   const char *p = data.c_str();
   size_t length = data.length();
   do {
-    int n = ::write(fd, p, length);
+    int n = TEMP_FAILURE_RETRY(write(fd, p, length));
+    if (n < 0) {
+      PLOG(WARNING) << "Failed to write to descriptor: " << fd;
+      return false;
+    }
     p += n;
     length -= n;
   } while (length > 0);
+  return true;
 }
 
 static constexpr const char kFieldSeparator = ',';
@@ -137,13 +110,8 @@
  *    /system/priv-app/app/app.apk,131232145,11,23,454,54
  *    /system/priv-app/app/app.apk:classes5.dex,218490184,39,13,49,1
  **/
-bool ProfileCompilationInfo::Save(const std::string& filename) {
-  int fd = OpenFile(filename, READ_WRITE);
-  if (fd == -1) {
-    return false;
-  }
-
-  // TODO(calin): Merge with a previous existing profile.
+bool ProfileCompilationInfo::Save(uint32_t fd) {
+  DCHECK_GE(fd, 0u);
   // TODO(calin): Profile this and see how much memory it takes. If too much,
   // write to file directly.
   std::ostringstream os;
@@ -158,9 +126,7 @@
     os << kLineSeparator;
   }
 
-  WriteToFile(fd, os);
-
-  return CloseDescriptorForFile(fd, filename);
+  return WriteToFile(fd, os);
 }
 
 // TODO(calin): This a duplicate of Utils::Split fixing the case where the first character
@@ -222,7 +188,9 @@
       LOG(WARNING) << "Cannot parse method_idx " << parts[i];
       return false;
     }
-    AddData(dex_location, checksum, method_idx);
+    if (!AddData(dex_location, checksum, method_idx)) {
+      return false;
+    }
   }
   return true;
 }
@@ -249,23 +217,18 @@
   return new_line_pos == -1 ? new_line_pos : new_line_pos + 1;
 }
 
-bool ProfileCompilationInfo::Load(const std::string& filename) {
-  int fd = OpenFile(filename, READ);
-  if (fd == -1) {
-    return false;
-  }
+bool ProfileCompilationInfo::Load(uint32_t fd) {
+  DCHECK_GE(fd, 0u);
 
   std::string current_line;
   const int kBufferSize = 1024;
   char buffer[kBufferSize];
-  bool success = true;
 
-  while (success) {
-    int n = read(fd, buffer, kBufferSize);
+  while (true) {
+    int n = TEMP_FAILURE_RETRY(read(fd, buffer, kBufferSize));
     if (n < 0) {
-      PLOG(WARNING) << "Error when reading profile file " << filename;
-      success = false;
-      break;
+      PLOG(WARNING) << "Error when reading profile file";
+      return false;
     } else if (n == 0) {
       break;
     }
@@ -278,17 +241,13 @@
         break;
       }
       if (!ProcessLine(current_line)) {
-        success = false;
-        break;
+        return false;
       }
       // Reset the current line (we just processed it).
       current_line.clear();
     }
   }
-  if (!success) {
-    info_.clear();
-  }
-  return CloseDescriptorForFile(fd, filename) && success;
+  return true;
 }
 
 bool ProfileCompilationInfo::Load(const ProfileCompilationInfo& other) {
@@ -369,4 +328,8 @@
   return os.str();
 }
 
+bool ProfileCompilationInfo::Equals(ProfileCompilationInfo& other) {
+  return info_.Equals(other.info_);
+}
+
 }  // namespace art
diff --git a/runtime/jit/offline_profiling_info.h b/runtime/jit/offline_profiling_info.h
index 26e1ac3..ffd1433 100644
--- a/runtime/jit/offline_profiling_info.h
+++ b/runtime/jit/offline_profiling_info.h
@@ -39,15 +39,18 @@
  */
 class ProfileCompilationInfo {
  public:
+  // Saves profile information about the given methods in the given file.
+  // Note that the saving proceeds only if the file can be locked for exclusive access.
+  // If not (the locking is not blocking), the function does not save and returns false.
   static bool SaveProfilingInfo(const std::string& filename,
                                 const std::vector<ArtMethod*>& methods);
 
-  // Loads profile information from the given file.
-  bool Load(const std::string& profile_filename);
+  // Loads profile information from the given file descriptor.
+  bool Load(uint32_t fd);
   // Loads the data from another ProfileCompilationInfo object.
   bool Load(const ProfileCompilationInfo& info);
-  // Saves the profile data to the given file.
-  bool Save(const std::string& profile_filename);
+  // Saves the profile data to the given file descriptor.
+  bool Save(uint32_t fd);
   // Returns the number of methods that were profiled.
   uint32_t GetNumberOfMethods() const;
 
@@ -61,6 +64,9 @@
   std::string DumpInfo(const std::vector<const DexFile*>* dex_files,
                        bool print_full_dex_location = true) const;
 
+  // For testing purposes.
+  bool Equals(ProfileCompilationInfo& other);
+
  private:
   bool AddData(const std::string& dex_location, uint32_t checksum, uint16_t method_idx);
   bool ProcessLine(const std::string& line);
@@ -69,10 +75,18 @@
     explicit DexFileData(uint32_t location_checksum) : checksum(location_checksum) {}
     uint32_t checksum;
     std::set<uint16_t> method_set;
+
+    bool operator==(const DexFileData& other) const {
+      return checksum == other.checksum && method_set == other.method_set;
+    }
   };
 
   using DexFileToProfileInfoMap = SafeMap<const std::string, DexFileData>;
 
+  friend class ProfileCompilationInfoTest;
+  friend class CompilerDriverProfileTest;
+  friend class ProfileAssistantTest;
+
   DexFileToProfileInfoMap info_;
 };
 
diff --git a/runtime/jit/profile_compilation_info_test.cc b/runtime/jit/profile_compilation_info_test.cc
new file mode 100644
index 0000000..482ea06
--- /dev/null
+++ b/runtime/jit/profile_compilation_info_test.cc
@@ -0,0 +1,166 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <gtest/gtest.h>
+
+#include "base/unix_file/fd_file.h"
+#include "art_method-inl.h"
+#include "class_linker-inl.h"
+#include "common_runtime_test.h"
+#include "dex_file.h"
+#include "mirror/class-inl.h"
+#include "mirror/class_loader.h"
+#include "handle_scope-inl.h"
+#include "jit/offline_profiling_info.h"
+#include "scoped_thread_state_change.h"
+
+namespace art {
+
+class ProfileCompilationInfoTest : public CommonRuntimeTest {
+ protected:
+  std::vector<ArtMethod*> GetVirtualMethods(jobject class_loader,
+                                            const std::string& clazz) {
+    ClassLinker* class_linker = Runtime::Current()->GetClassLinker();
+    Thread* self = Thread::Current();
+    ScopedObjectAccess soa(self);
+    StackHandleScope<1> hs(self);
+    Handle<mirror::ClassLoader> h_loader(hs.NewHandle(
+        reinterpret_cast<mirror::ClassLoader*>(self->DecodeJObject(class_loader))));
+    mirror::Class* klass = class_linker->FindClass(self, clazz.c_str(), h_loader);
+
+    const auto pointer_size = class_linker->GetImagePointerSize();
+    std::vector<ArtMethod*> methods;
+    for (auto& m : klass->GetVirtualMethods(pointer_size)) {
+      methods.push_back(&m);
+    }
+    return methods;
+  }
+
+  bool AddData(const std::string& dex_location,
+               uint32_t checksum,
+               uint16_t method_index,
+               ProfileCompilationInfo* info) {
+    return info->AddData(dex_location, checksum, method_index);
+  }
+
+  uint32_t GetFd(const ScratchFile& file) {
+    return static_cast<uint32_t>(file.GetFd());
+  }
+};
+
+TEST_F(ProfileCompilationInfoTest, SaveArtMethods) {
+  ScratchFile profile;
+
+  Thread* self = Thread::Current();
+  jobject class_loader;
+  {
+    ScopedObjectAccess soa(self);
+    class_loader = LoadDex("ProfileTestMultiDex");
+  }
+  ASSERT_NE(class_loader, nullptr);
+
+  // Save virtual methods from Main.
+  std::vector<ArtMethod*> main_methods = GetVirtualMethods(class_loader, "LMain;");
+  ASSERT_TRUE(ProfileCompilationInfo::SaveProfilingInfo(profile.GetFilename(), main_methods));
+
+  // Check that what we saved is in the profile.
+  ProfileCompilationInfo info1;
+  ASSERT_TRUE(info1.Load(GetFd(profile)));
+  ASSERT_EQ(info1.GetNumberOfMethods(), main_methods.size());
+  {
+    ScopedObjectAccess soa(self);
+    for (ArtMethod* m : main_methods) {
+      ASSERT_TRUE(info1.ContainsMethod(MethodReference(m->GetDexFile(), m->GetDexMethodIndex())));
+    }
+  }
+
+  // Save virtual methods from Second.
+  std::vector<ArtMethod*> second_methods = GetVirtualMethods(class_loader, "LSecond;");
+  ASSERT_TRUE(ProfileCompilationInfo::SaveProfilingInfo(profile.GetFilename(), second_methods));
+
+  // Check that what we saved is in the profile (methods form Main and Second).
+  ProfileCompilationInfo info2;
+  ASSERT_TRUE(profile.GetFile()->ResetOffset());
+  ASSERT_TRUE(info2.Load(GetFd(profile)));
+  ASSERT_EQ(info2.GetNumberOfMethods(), main_methods.size() + second_methods.size());
+  {
+    ScopedObjectAccess soa(self);
+    for (ArtMethod* m : main_methods) {
+      ASSERT_TRUE(info2.ContainsMethod(MethodReference(m->GetDexFile(), m->GetDexMethodIndex())));
+    }
+    for (ArtMethod* m : second_methods) {
+      ASSERT_TRUE(info2.ContainsMethod(MethodReference(m->GetDexFile(), m->GetDexMethodIndex())));
+    }
+  }
+}
+
+TEST_F(ProfileCompilationInfoTest, SaveFd) {
+  ScratchFile profile;
+
+  ProfileCompilationInfo saved_info;
+  // Save a few methods.
+  for (uint16_t i = 0; i < 10; i++) {
+    ASSERT_TRUE(AddData("dex_location1", /* checksum */ 1, /* method_idx */ i, &saved_info));
+    ASSERT_TRUE(AddData("dex_location2", /* checksum */ 2, /* method_idx */ i, &saved_info));
+  }
+  ASSERT_TRUE(saved_info.Save(GetFd(profile)));
+  ASSERT_EQ(0, profile.GetFile()->Flush());
+
+  // Check that we get back what we saved.
+  ProfileCompilationInfo loaded_info;
+  ASSERT_TRUE(profile.GetFile()->ResetOffset());
+  ASSERT_TRUE(loaded_info.Load(GetFd(profile)));
+  ASSERT_TRUE(loaded_info.Equals(saved_info));
+
+  // Save more methods.
+  for (uint16_t i = 0; i < 100; i++) {
+    ASSERT_TRUE(AddData("dex_location1", /* checksum */ 1, /* method_idx */ i, &saved_info));
+    ASSERT_TRUE(AddData("dex_location2", /* checksum */ 2, /* method_idx */ i, &saved_info));
+    ASSERT_TRUE(AddData("dex_location3", /* checksum */ 3, /* method_idx */ i, &saved_info));
+  }
+  ASSERT_TRUE(profile.GetFile()->ResetOffset());
+  ASSERT_TRUE(saved_info.Save(GetFd(profile)));
+  ASSERT_EQ(0, profile.GetFile()->Flush());
+
+  // Check that we get back everything we saved.
+  ProfileCompilationInfo loaded_info2;
+  ASSERT_TRUE(profile.GetFile()->ResetOffset());
+  ASSERT_TRUE(loaded_info2.Load(GetFd(profile)));
+  ASSERT_TRUE(loaded_info2.Equals(saved_info));
+}
+
+TEST_F(ProfileCompilationInfoTest, AddDataFail) {
+  ScratchFile profile;
+
+  ProfileCompilationInfo info;
+  ASSERT_TRUE(AddData("dex_location", /* checksum */ 1, /* method_idx */ 1, &info));
+  // Trying to add info for an existing file but with a different checksum.
+  ASSERT_FALSE(AddData("dex_location", /* checksum */ 2, /* method_idx */ 2, &info));
+}
+
+TEST_F(ProfileCompilationInfoTest, LoadFail) {
+  ScratchFile profile;
+
+  ProfileCompilationInfo info1;
+  ASSERT_TRUE(AddData("dex_location", /* checksum */ 1, /* method_idx */ 1, &info1));
+  // Use the same file, change the checksum.
+  ProfileCompilationInfo info2;
+  ASSERT_TRUE(AddData("dex_location", /* checksum */ 2, /* method_idx */ 2, &info2));
+
+  ASSERT_FALSE(info1.Load(info2));
+}
+
+}  // namespace art
diff --git a/runtime/jit/profile_saver.cc b/runtime/jit/profile_saver.cc
index ec289ea..fc257c0 100644
--- a/runtime/jit/profile_saver.cc
+++ b/runtime/jit/profile_saver.cc
@@ -86,12 +86,14 @@
 }
 
 bool ProfileSaver::ProcessProfilingInfo() {
-  VLOG(profiler) << "Initiating save profiling information to: " << output_filename_;
+  VLOG(profiler) << "Save profiling information to: " << output_filename_;
 
   uint64_t last_update_time_ns = jit_code_cache_->GetLastUpdateTimeNs();
   if (last_update_time_ns - code_cache_last_update_time_ns_
-      > kMinimumTimeBetweenCodeCacheUpdatesNs) {
-    VLOG(profiler) << "Not enough time has passed since the last code cache update.";
+      < kMinimumTimeBetweenCodeCacheUpdatesNs) {
+    VLOG(profiler) << "Not enough time has passed since the last code cache update."
+        << "Last update: " << last_update_time_ns
+        << " Last save: " << code_cache_last_update_time_ns_;
     return false;
   }
 
diff --git a/test/ProfileTestMultiDex/Main.java b/test/ProfileTestMultiDex/Main.java
new file mode 100644
index 0000000..41532ea
--- /dev/null
+++ b/test/ProfileTestMultiDex/Main.java
@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+class Main {
+  public String getA() {
+    return "A";
+  }
+  public String getB() {
+    return "B";
+  }
+  public String getC() {
+    return "C";
+  }
+}
diff --git a/test/ProfileTestMultiDex/Second.java b/test/ProfileTestMultiDex/Second.java
new file mode 100644
index 0000000..4ac5abc
--- /dev/null
+++ b/test/ProfileTestMultiDex/Second.java
@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+class Second {
+  public String getX() {
+    return "X";
+  }
+  public String getY() {
+    return "Y";
+  }
+  public String getZ() {
+    return "Z";
+  }
+}
diff --git a/test/ProfileTestMultiDex/main.jpp b/test/ProfileTestMultiDex/main.jpp
new file mode 100644
index 0000000..f2e3b4e
--- /dev/null
+++ b/test/ProfileTestMultiDex/main.jpp
@@ -0,0 +1,3 @@
+main:
+  @@com.android.jack.annotations.ForceInMainDex
+  class Second
diff --git a/test/ProfileTestMultiDex/main.list b/test/ProfileTestMultiDex/main.list
new file mode 100644
index 0000000..44ba78e
--- /dev/null
+++ b/test/ProfileTestMultiDex/main.list
@@ -0,0 +1 @@
+Main.class