Use the lock word bits for Baker-style read barrier.
This enables the standard object header to be used with the
Baker-style read barrier.
Bug: 19355854
Bug: 12687968
Change-Id: Ie552b6e1dfe30e96cb1d0895bd0dff25f9d7d015
diff --git a/runtime/asm_support.h b/runtime/asm_support.h
index 8057dd1..13921e7 100644
--- a/runtime/asm_support.h
+++ b/runtime/asm_support.h
@@ -124,7 +124,7 @@
#define MIRROR_OBJECT_LOCK_WORD_OFFSET 4
ADD_TEST_EQ(MIRROR_OBJECT_LOCK_WORD_OFFSET, art::mirror::Object::MonitorOffset().Int32Value())
-#if defined(USE_BAKER_OR_BROOKS_READ_BARRIER)
+#if defined(USE_BROOKS_READ_BARRIER)
#define MIRROR_OBJECT_HEADER_SIZE 16
#else
#define MIRROR_OBJECT_HEADER_SIZE 8
diff --git a/runtime/class_linker_test.cc b/runtime/class_linker_test.cc
index 7bee98f..5239d44 100644
--- a/runtime/class_linker_test.cc
+++ b/runtime/class_linker_test.cc
@@ -479,7 +479,7 @@
ObjectOffsets() : CheckOffsets<mirror::Object>(false, "Ljava/lang/Object;") {
addOffset(OFFSETOF_MEMBER(mirror::Object, klass_), "shadow$_klass_");
addOffset(OFFSETOF_MEMBER(mirror::Object, monitor_), "shadow$_monitor_");
-#ifdef USE_BAKER_OR_BROOKS_READ_BARRIER
+#ifdef USE_BROOKS_READ_BARRIER
addOffset(OFFSETOF_MEMBER(mirror::Object, x_rb_ptr_), "shadow$_x_rb_ptr_");
addOffset(OFFSETOF_MEMBER(mirror::Object, x_xpadding_), "shadow$_x_xpadding_");
#endif
@@ -736,14 +736,14 @@
EXPECT_FALSE(JavaLangObject->IsSynthetic());
EXPECT_EQ(2U, JavaLangObject->NumDirectMethods());
EXPECT_EQ(11U, JavaLangObject->NumVirtualMethods());
- if (!kUseBakerOrBrooksReadBarrier) {
+ if (!kUseBrooksReadBarrier) {
EXPECT_EQ(2U, JavaLangObject->NumInstanceFields());
} else {
EXPECT_EQ(4U, JavaLangObject->NumInstanceFields());
}
EXPECT_STREQ(JavaLangObject->GetInstanceField(0)->GetName(), "shadow$_klass_");
EXPECT_STREQ(JavaLangObject->GetInstanceField(1)->GetName(), "shadow$_monitor_");
- if (kUseBakerOrBrooksReadBarrier) {
+ if (kUseBrooksReadBarrier) {
EXPECT_STREQ(JavaLangObject->GetInstanceField(2)->GetName(), "shadow$_x_rb_ptr_");
EXPECT_STREQ(JavaLangObject->GetInstanceField(3)->GetName(), "shadow$_x_xpadding_");
}
diff --git a/runtime/gc/collector/concurrent_copying.cc b/runtime/gc/collector/concurrent_copying.cc
index eabb1c2..26f349a 100644
--- a/runtime/gc/collector/concurrent_copying.cc
+++ b/runtime/gc/collector/concurrent_copying.cc
@@ -718,6 +718,7 @@
// Leave References gray so that GetReferent() will trigger RB.
CHECK(to_ref->AsReference()->IsEnqueued()) << "Left unenqueued ref gray " << to_ref;
} else {
+#ifdef USE_BAKER_OR_BROOKS_READ_BARRIER
if (kUseBakerReadBarrier) {
if (region_space_->IsInToSpace(to_ref)) {
// If to-space, change from gray to white.
@@ -739,6 +740,9 @@
CHECK(to_ref->GetReadBarrierPointer() == ReadBarrier::BlackPtr());
}
}
+#else
+ DCHECK(!kUseBakerReadBarrier);
+#endif
}
if (ReadBarrier::kEnableToSpaceInvariantChecks || kIsDebugBuild) {
ConcurrentCopyingAssertToSpaceInvariantObjectVisitor visitor(this);
@@ -815,7 +819,7 @@
DCHECK(obj != nullptr);
DCHECK(collector_->heap_->GetMarkBitmap()->Test(obj)) << obj;
DCHECK_EQ(obj->GetReadBarrierPointer(), ReadBarrier::BlackPtr()) << obj;
- obj->SetReadBarrierPointer(ReadBarrier::WhitePtr());
+ obj->AtomicSetReadBarrierPointer(ReadBarrier::BlackPtr(), ReadBarrier::WhitePtr());
DCHECK_EQ(obj->GetReadBarrierPointer(), ReadBarrier::WhitePtr()) << obj;
}
@@ -963,7 +967,8 @@
if (kUseBakerReadBarrier) {
DCHECK_EQ(ref->GetReadBarrierPointer(), ReadBarrier::BlackPtr()) << ref;
// Clear the black ptr.
- ref->SetReadBarrierPointer(ReadBarrier::WhitePtr());
+ ref->AtomicSetReadBarrierPointer(ReadBarrier::BlackPtr(), ReadBarrier::WhitePtr());
+ DCHECK_EQ(ref->GetReadBarrierPointer(), ReadBarrier::WhitePtr()) << ref;
}
size_t obj_size = ref->SizeOf();
size_t alloc_size = RoundUp(obj_size, space::RegionSpace::kAlignment);
@@ -1330,10 +1335,6 @@
while (true) {
// Copy the object. TODO: copy only the lockword in the second iteration and on?
memcpy(to_ref, from_ref, obj_size);
- // Set the gray ptr.
- if (kUseBakerReadBarrier) {
- to_ref->SetReadBarrierPointer(ReadBarrier::GrayPtr());
- }
LockWord old_lock_word = to_ref->GetLockWord(false);
@@ -1378,6 +1379,11 @@
return to_ref;
}
+ // Set the gray ptr.
+ if (kUseBakerReadBarrier) {
+ to_ref->SetReadBarrierPointer(ReadBarrier::GrayPtr());
+ }
+
LockWord new_lock_word = LockWord::FromForwardingAddress(reinterpret_cast<size_t>(to_ref));
// Try to atomically write the fwd ptr.
@@ -1484,6 +1490,21 @@
}
DCHECK(from_ref != nullptr);
DCHECK(heap_->collector_type_ == kCollectorTypeCC);
+ if (kUseBakerReadBarrier && !is_active_) {
+ // In the lock word forward address state, the read barrier bits
+ // in the lock word are part of the stored forwarding address and
+ // invalid. This is usually OK as the from-space copy of objects
+ // aren't accessed by mutators due to the to-space
+ // invariant. However, during the dex2oat image writing relocation
+ // and the zygote compaction, objects can be in the forward
+ // address state (to store the forward/relocation addresses) and
+ // they can still be accessed and the invalid read barrier bits
+ // are consulted. If they look like gray but aren't really, the
+ // read barriers slow path can trigger when it shouldn't. To guard
+ // against this, return here if the CC collector isn't running.
+ return from_ref;
+ }
+ DCHECK(region_space_ != nullptr) << "Read barrier slow path taken when CC isn't running?";
space::RegionSpace::RegionType rtype = region_space_->GetRegionType(from_ref);
if (rtype == space::RegionSpace::RegionType::kRegionTypeToSpace) {
// It's already marked.
diff --git a/runtime/gc/collector/semi_space-inl.h b/runtime/gc/collector/semi_space-inl.h
index 922a71c..7b19dc9 100644
--- a/runtime/gc/collector/semi_space-inl.h
+++ b/runtime/gc/collector/semi_space-inl.h
@@ -60,10 +60,6 @@
if (obj == nullptr) {
return;
}
- if (kUseBakerOrBrooksReadBarrier) {
- // Verify all the objects have the correct forward pointer installed.
- obj->AssertReadBarrierPointer();
- }
if (from_space_->HasAddress(obj)) {
mirror::Object* forward_address = GetForwardingAddressInFromSpace(obj);
// If the object has already been moved, return the new forward address.
diff --git a/runtime/gc/reference_queue.cc b/runtime/gc/reference_queue.cc
index 4c93a4c..4ba3983 100644
--- a/runtime/gc/reference_queue.cc
+++ b/runtime/gc/reference_queue.cc
@@ -96,11 +96,11 @@
<< "ref=" << ref << " rb_ptr=" << ref->GetReadBarrierPointer();
if (heap->ConcurrentCopyingCollector()->RegionSpace()->IsInToSpace(ref)) {
// Moving objects.
- ref->SetReadBarrierPointer(ReadBarrier::WhitePtr());
+ ref->AtomicSetReadBarrierPointer(ReadBarrier::GrayPtr(), ReadBarrier::WhitePtr());
CHECK_EQ(ref->GetReadBarrierPointer(), ReadBarrier::WhitePtr());
} else {
// Non-moving objects.
- ref->SetReadBarrierPointer(ReadBarrier::BlackPtr());
+ ref->AtomicSetReadBarrierPointer(ReadBarrier::GrayPtr(), ReadBarrier::BlackPtr());
CHECK_EQ(ref->GetReadBarrierPointer(), ReadBarrier::BlackPtr());
}
}
diff --git a/runtime/lock_word-inl.h b/runtime/lock_word-inl.h
index d831bfb..341501b 100644
--- a/runtime/lock_word-inl.h
+++ b/runtime/lock_word-inl.h
@@ -53,6 +53,7 @@
inline LockWord::LockWord(Monitor* mon, uint32_t rb_state)
: value_(mon->GetMonitorId() | (rb_state << kReadBarrierStateShift) |
(kStateFat << kStateShift)) {
+ DCHECK_EQ(rb_state & ~kReadBarrierStateMask, 0U);
#ifndef __LP64__
DCHECK_ALIGNED(mon, kMonitorIdAlignment);
#endif
diff --git a/runtime/lock_word.h b/runtime/lock_word.h
index 46c3bd4..655aa3a 100644
--- a/runtime/lock_word.h
+++ b/runtime/lock_word.h
@@ -94,6 +94,7 @@
kReadBarrierStateMaskShiftedToggled = ~kReadBarrierStateMaskShifted,
// When the state is kHashCode, the non-state bits hold the hashcode.
+ // Note Object.hashCode() has the hash code layout hardcoded.
kHashShift = 0,
kHashSize = 32 - kStateSize - kReadBarrierStateSize,
kHashMask = (1 << kHashSize) - 1,
@@ -110,6 +111,7 @@
static LockWord FromThinLockId(uint32_t thread_id, uint32_t count, uint32_t rb_state) {
CHECK_LE(thread_id, static_cast<uint32_t>(kThinLockMaxOwner));
CHECK_LE(count, static_cast<uint32_t>(kThinLockMaxCount));
+ DCHECK_EQ(rb_state & ~kReadBarrierStateMask, 0U);
return LockWord((thread_id << kThinLockOwnerShift) | (count << kThinLockCountShift) |
(rb_state << kReadBarrierStateShift) |
(kStateThinOrUnlocked << kStateShift));
@@ -122,12 +124,14 @@
static LockWord FromHashCode(uint32_t hash_code, uint32_t rb_state) {
CHECK_LE(hash_code, static_cast<uint32_t>(kMaxHash));
+ DCHECK_EQ(rb_state & ~kReadBarrierStateMask, 0U);
return LockWord((hash_code << kHashShift) |
(rb_state << kReadBarrierStateShift) |
(kStateHash << kStateShift));
}
static LockWord FromDefault(uint32_t rb_state) {
+ DCHECK_EQ(rb_state & ~kReadBarrierStateMask, 0U);
return LockWord(rb_state << kReadBarrierStateShift);
}
@@ -149,7 +153,8 @@
LockState GetState() const {
CheckReadBarrierState();
- if (UNLIKELY(value_ == 0)) {
+ if ((!kUseReadBarrier && UNLIKELY(value_ == 0)) ||
+ (kUseReadBarrier && UNLIKELY((value_ & kReadBarrierStateMaskShiftedToggled) == 0))) {
return kUnlocked;
} else {
uint32_t internal_state = (value_ >> kStateShift) & kStateMask;
@@ -171,6 +176,14 @@
return (value_ >> kReadBarrierStateShift) & kReadBarrierStateMask;
}
+ void SetReadBarrierState(uint32_t rb_state) {
+ DCHECK_EQ(rb_state & ~kReadBarrierStateMask, 0U);
+ DCHECK_NE(static_cast<uint32_t>(GetState()), static_cast<uint32_t>(kForwardingAddress));
+ // Clear and or the bits.
+ value_ &= ~(kReadBarrierStateMask << kReadBarrierStateShift);
+ value_ |= (rb_state & kReadBarrierStateMask) << kReadBarrierStateShift;
+ }
+
// Return the owner thin lock thread id.
uint32_t ThinLockOwner() const;
diff --git a/runtime/mirror/object-inl.h b/runtime/mirror/object-inl.h
index 2581fad..95c1d11 100644
--- a/runtime/mirror/object-inl.h
+++ b/runtime/mirror/object-inl.h
@@ -115,8 +115,11 @@
}
inline Object* Object::GetReadBarrierPointer() {
-#ifdef USE_BAKER_OR_BROOKS_READ_BARRIER
- DCHECK(kUseBakerOrBrooksReadBarrier);
+#ifdef USE_BAKER_READ_BARRIER
+ DCHECK(kUseBakerReadBarrier);
+ return reinterpret_cast<Object*>(GetLockWord(false).ReadBarrierState());
+#elif USE_BROOKS_READ_BARRIER
+ DCHECK(kUseBrooksReadBarrier);
return GetFieldObject<Object, kVerifyNone, kWithoutReadBarrier>(
OFFSET_OF_OBJECT_MEMBER(Object, x_rb_ptr_));
#else
@@ -126,8 +129,14 @@
}
inline void Object::SetReadBarrierPointer(Object* rb_ptr) {
-#ifdef USE_BAKER_OR_BROOKS_READ_BARRIER
- DCHECK(kUseBakerOrBrooksReadBarrier);
+#ifdef USE_BAKER_READ_BARRIER
+ DCHECK(kUseBakerReadBarrier);
+ DCHECK_EQ(reinterpret_cast<uint64_t>(rb_ptr) >> 32, 0U);
+ LockWord lw = GetLockWord(false);
+ lw.SetReadBarrierState(static_cast<uint32_t>(reinterpret_cast<uintptr_t>(rb_ptr)));
+ SetLockWord(lw, false);
+#elif USE_BROOKS_READ_BARRIER
+ DCHECK(kUseBrooksReadBarrier);
// We don't mark the card as this occurs as part of object allocation. Not all objects have
// backing cards, such as large objects.
SetFieldObjectWithoutWriteBarrier<false, false, kVerifyNone>(
@@ -140,8 +149,27 @@
}
inline bool Object::AtomicSetReadBarrierPointer(Object* expected_rb_ptr, Object* rb_ptr) {
-#ifdef USE_BAKER_OR_BROOKS_READ_BARRIER
- DCHECK(kUseBakerOrBrooksReadBarrier);
+#ifdef USE_BAKER_READ_BARRIER
+ DCHECK(kUseBakerReadBarrier);
+ DCHECK_EQ(reinterpret_cast<uint64_t>(expected_rb_ptr) >> 32, 0U);
+ DCHECK_EQ(reinterpret_cast<uint64_t>(rb_ptr) >> 32, 0U);
+ LockWord expected_lw;
+ LockWord new_lw;
+ do {
+ LockWord lw = GetLockWord(false);
+ if (UNLIKELY(reinterpret_cast<Object*>(lw.ReadBarrierState()) != expected_rb_ptr)) {
+ // Lost the race.
+ return false;
+ }
+ expected_lw = lw;
+ expected_lw.SetReadBarrierState(
+ static_cast<uint32_t>(reinterpret_cast<uintptr_t>(expected_rb_ptr)));
+ new_lw = lw;
+ new_lw.SetReadBarrierState(static_cast<uint32_t>(reinterpret_cast<uintptr_t>(rb_ptr)));
+ } while (!CasLockWordWeakSequentiallyConsistent(expected_lw, new_lw));
+ return true;
+#elif USE_BROOKS_READ_BARRIER
+ DCHECK(kUseBrooksReadBarrier);
MemberOffset offset = OFFSET_OF_OBJECT_MEMBER(Object, x_rb_ptr_);
uint8_t* raw_addr = reinterpret_cast<uint8_t*>(this) + offset.SizeValue();
Atomic<uint32_t>* atomic_rb_ptr = reinterpret_cast<Atomic<uint32_t>*>(raw_addr);
diff --git a/runtime/mirror/object.h b/runtime/mirror/object.h
index 343c9bc..7f162b7 100644
--- a/runtime/mirror/object.h
+++ b/runtime/mirror/object.h
@@ -62,7 +62,7 @@
static constexpr bool kCheckFieldAssignments = false;
// Size of Object.
-static constexpr uint32_t kObjectHeaderSize = kUseBakerOrBrooksReadBarrier ? 16 : 8;
+static constexpr uint32_t kObjectHeaderSize = kUseBrooksReadBarrier ? 16 : 8;
// C++ mirror of java.lang.Object
class MANAGED LOCKABLE Object {
@@ -94,6 +94,9 @@
NO_RETURN
#endif
void SetReadBarrierPointer(Object* rb_ptr) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
+#ifndef USE_BAKER_OR_BROOKS_READ_BARRIER
+ NO_RETURN
+#endif
bool AtomicSetReadBarrierPointer(Object* expected_rb_ptr, Object* rb_ptr)
SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
void AssertReadBarrierPointer() const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
@@ -502,11 +505,11 @@
// Monitor and hash code information.
uint32_t monitor_;
-#ifdef USE_BAKER_OR_BROOKS_READ_BARRIER
+#ifdef USE_BROOKS_READ_BARRIER
// Note names use a 'x' prefix and the x_rb_ptr_ is of type int
// instead of Object to go with the alphabetical/by-type field order
// on the Java side.
- uint32_t x_rb_ptr_; // For the Baker or Brooks pointer.
+ uint32_t x_rb_ptr_; // For the Brooks pointer.
uint32_t x_xpadding_; // For 8-byte alignment. TODO: get rid of this.
#endif
