Hide content of pthread_cond_t in pthread_cond_internal_t.
Bug: 19249079
Change-Id: I6f55af30bcd6211ce71630c6cacbef0e1663dcee
diff --git a/libc/bionic/pthread_cond.cpp b/libc/bionic/pthread_cond.cpp
index 5542c59..cb7cf5f 100644
--- a/libc/bionic/pthread_cond.cpp
+++ b/libc/bionic/pthread_cond.cpp
@@ -41,6 +41,13 @@
#include "private/bionic_time_conversions.h"
#include "private/bionic_tls.h"
+// XXX *technically* there is a race condition that could allow
+// XXX a signal to be missed. If thread A is preempted in _wait()
+// XXX after unlocking the mutex and before waiting, and if other
+// XXX threads call signal or broadcast UINT_MAX/2 times (exactly),
+// XXX before thread A is scheduled again and calls futex_wait(),
+// XXX then the signal will be lost.
+
// We use one bit in pthread_condattr_t (long) values as the 'shared' flag
// and one bit for the clock type (CLOCK_REALTIME is ((clockid_t) 1), and
// CLOCK_MONOTONIC is ((clockid_t) 0).). The rest of the bits are a counter.
@@ -57,7 +64,6 @@
#define COND_GET_CLOCK(c) (((c) & COND_CLOCK_MASK) >> 1)
#define COND_SET_CLOCK(attr, c) ((attr) | (c << 1))
-
int pthread_condattr_init(pthread_condattr_t* attr) {
*attr = 0;
*attr |= PTHREAD_PROCESS_PRIVATE;
@@ -98,47 +104,50 @@
return 0;
}
-static inline atomic_uint* COND_TO_ATOMIC_POINTER(pthread_cond_t* cond) {
- static_assert(sizeof(atomic_uint) == sizeof(cond->value),
- "cond->value should actually be atomic_uint in implementation.");
+struct pthread_cond_internal_t {
+ atomic_uint state;
- // We prefer casting to atomic_uint instead of declaring cond->value to be atomic_uint directly.
- // Because using the second method pollutes pthread.h, and causes an error when compiling libcxx.
- return reinterpret_cast<atomic_uint*>(&cond->value);
+ bool process_shared() const {
+ return COND_IS_SHARED(atomic_load_explicit(&state, memory_order_relaxed));
+ }
+
+ int get_clock() const {
+ return COND_GET_CLOCK(atomic_load_explicit(&state, memory_order_relaxed));
+ }
+
+#if defined(__LP64__)
+ char __reserved[44];
+#endif
+};
+
+static pthread_cond_internal_t* __get_internal_cond(pthread_cond_t* cond_interface) {
+ static_assert(sizeof(pthread_cond_t) == sizeof(pthread_cond_internal_t),
+ "pthread_cond_t should actually be pthread_cond_internal_t in implementation.");
+ return reinterpret_cast<pthread_cond_internal_t*>(cond_interface);
}
-// XXX *technically* there is a race condition that could allow
-// XXX a signal to be missed. If thread A is preempted in _wait()
-// XXX after unlocking the mutex and before waiting, and if other
-// XXX threads call signal or broadcast UINT_MAX/2 times (exactly),
-// XXX before thread A is scheduled again and calls futex_wait(),
-// XXX then the signal will be lost.
+int pthread_cond_init(pthread_cond_t* cond_interface, const pthread_condattr_t* attr) {
+ pthread_cond_internal_t* cond = __get_internal_cond(cond_interface);
-int pthread_cond_init(pthread_cond_t* cond, const pthread_condattr_t* attr) {
- atomic_uint* cond_value_ptr = COND_TO_ATOMIC_POINTER(cond);
- unsigned int init_value = 0;
-
+ unsigned int init_state = 0;
if (attr != NULL) {
- init_value = (*attr & COND_FLAGS_MASK);
+ init_state = (*attr & COND_FLAGS_MASK);
}
- atomic_init(cond_value_ptr, init_value);
+ atomic_init(&cond->state, init_state);
return 0;
}
-int pthread_cond_destroy(pthread_cond_t* cond) {
- atomic_uint* cond_value_ptr = COND_TO_ATOMIC_POINTER(cond);
- atomic_store_explicit(cond_value_ptr, 0xdeadc04d, memory_order_relaxed);
+int pthread_cond_destroy(pthread_cond_t* cond_interface) {
+ pthread_cond_internal_t* cond = __get_internal_cond(cond_interface);
+ atomic_store_explicit(&cond->state, 0xdeadc04d, memory_order_relaxed);
return 0;
}
// This function is used by pthread_cond_broadcast and
// pthread_cond_signal to atomically decrement the counter
// then wake up thread_count threads.
-static int __pthread_cond_pulse(atomic_uint* cond_value_ptr, int thread_count) {
- unsigned int old_value = atomic_load_explicit(cond_value_ptr, memory_order_relaxed);
- bool shared = COND_IS_SHARED(old_value);
-
+static int __pthread_cond_pulse(pthread_cond_internal_t* cond, int thread_count) {
// We don't use a release/seq_cst fence here. Because pthread_cond_wait/signal can't be
// used as a method for memory synchronization by itself. It should always be used with
// pthread mutexes. Note that Spurious wakeups from pthread_cond_wait/timedwait may occur,
@@ -149,20 +158,18 @@
// synchronization. And it doesn't help even if we use any fence here.
// The increase of value should leave flags alone, even if the value can overflows.
- atomic_fetch_add_explicit(cond_value_ptr, COND_COUNTER_STEP, memory_order_relaxed);
+ atomic_fetch_add_explicit(&cond->state, COND_COUNTER_STEP, memory_order_relaxed);
- __futex_wake_ex(cond_value_ptr, shared, thread_count);
+ __futex_wake_ex(&cond->state, cond->process_shared(), thread_count);
return 0;
}
-__LIBC_HIDDEN__
-int __pthread_cond_timedwait_relative(atomic_uint* cond_value_ptr, pthread_mutex_t* mutex,
- const timespec* reltime) {
- unsigned int old_value = atomic_load_explicit(cond_value_ptr, memory_order_relaxed);
- bool shared = COND_IS_SHARED(old_value);
+static int __pthread_cond_timedwait_relative(pthread_cond_internal_t* cond, pthread_mutex_t* mutex,
+ const timespec* rel_timeout_or_null) {
+ unsigned int old_state = atomic_load_explicit(&cond->state, memory_order_relaxed);
pthread_mutex_unlock(mutex);
- int status = __futex_wait_ex(cond_value_ptr, shared, old_value, reltime);
+ int status = __futex_wait_ex(&cond->state, cond->process_shared(), old_state, rel_timeout_or_null);
pthread_mutex_lock(mutex);
if (status == -ETIMEDOUT) {
@@ -171,67 +178,68 @@
return 0;
}
-__LIBC_HIDDEN__
-int __pthread_cond_timedwait(atomic_uint* cond_value_ptr, pthread_mutex_t* mutex,
- const timespec* abs_ts, clockid_t clock) {
+static int __pthread_cond_timedwait(pthread_cond_internal_t* cond, pthread_mutex_t* mutex,
+ const timespec* abs_timeout_or_null, clockid_t clock) {
timespec ts;
- timespec* tsp;
+ timespec* rel_timeout = NULL;
- if (abs_ts != NULL) {
- if (!timespec_from_absolute_timespec(ts, *abs_ts, clock)) {
+ if (abs_timeout_or_null != NULL) {
+ rel_timeout = &ts;
+ if (!timespec_from_absolute_timespec(*rel_timeout, *abs_timeout_or_null, clock)) {
return ETIMEDOUT;
}
- tsp = &ts;
- } else {
- tsp = NULL;
}
- return __pthread_cond_timedwait_relative(cond_value_ptr, mutex, tsp);
+ return __pthread_cond_timedwait_relative(cond, mutex, rel_timeout);
}
-int pthread_cond_broadcast(pthread_cond_t* cond) {
- atomic_uint* cond_value_ptr = COND_TO_ATOMIC_POINTER(cond);
- return __pthread_cond_pulse(cond_value_ptr, INT_MAX);
+int pthread_cond_broadcast(pthread_cond_t* cond_interface) {
+ return __pthread_cond_pulse(__get_internal_cond(cond_interface), INT_MAX);
}
-int pthread_cond_signal(pthread_cond_t* cond) {
- atomic_uint* cond_value_ptr = COND_TO_ATOMIC_POINTER(cond);
- return __pthread_cond_pulse(cond_value_ptr, 1);
+int pthread_cond_signal(pthread_cond_t* cond_interface) {
+ return __pthread_cond_pulse(__get_internal_cond(cond_interface), 1);
}
-int pthread_cond_wait(pthread_cond_t* cond, pthread_mutex_t* mutex) {
- atomic_uint* cond_value_ptr = COND_TO_ATOMIC_POINTER(cond);
- return __pthread_cond_timedwait(cond_value_ptr, mutex, NULL,
- COND_GET_CLOCK(atomic_load_explicit(cond_value_ptr, memory_order_relaxed)));
+int pthread_cond_wait(pthread_cond_t* cond_interface, pthread_mutex_t* mutex) {
+ pthread_cond_internal_t* cond = __get_internal_cond(cond_interface);
+ return __pthread_cond_timedwait(cond, mutex, NULL, cond->get_clock());
}
-int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t * mutex, const timespec *abstime) {
- atomic_uint* cond_value_ptr = COND_TO_ATOMIC_POINTER(cond);
- return __pthread_cond_timedwait(cond_value_ptr, mutex, abstime,
- COND_GET_CLOCK(atomic_load_explicit(cond_value_ptr, memory_order_relaxed)));
+int pthread_cond_timedwait(pthread_cond_t *cond_interface, pthread_mutex_t * mutex,
+ const timespec *abstime) {
+
+ pthread_cond_internal_t* cond = __get_internal_cond(cond_interface);
+ return __pthread_cond_timedwait(cond, mutex, abstime, cond->get_clock());
}
#if !defined(__LP64__)
// TODO: this exists only for backward binary compatibility on 32 bit platforms.
-extern "C" int pthread_cond_timedwait_monotonic(pthread_cond_t* cond, pthread_mutex_t* mutex, const timespec* abstime) {
- atomic_uint* cond_value_ptr = COND_TO_ATOMIC_POINTER(cond);
- return __pthread_cond_timedwait(cond_value_ptr, mutex, abstime, CLOCK_MONOTONIC);
+extern "C" int pthread_cond_timedwait_monotonic(pthread_cond_t* cond_interface,
+ pthread_mutex_t* mutex,
+ const timespec* abs_timeout) {
+
+ return __pthread_cond_timedwait(__get_internal_cond(cond_interface), mutex, abs_timeout,
+ CLOCK_MONOTONIC);
}
-extern "C" int pthread_cond_timedwait_monotonic_np(pthread_cond_t* cond, pthread_mutex_t* mutex, const timespec* abstime) {
- atomic_uint* cond_value_ptr = COND_TO_ATOMIC_POINTER(cond);
- return __pthread_cond_timedwait(cond_value_ptr, mutex, abstime, CLOCK_MONOTONIC);
+extern "C" int pthread_cond_timedwait_monotonic_np(pthread_cond_t* cond_interface,
+ pthread_mutex_t* mutex,
+ const timespec* abs_timeout) {
+ return pthread_cond_timedwait_monotonic(cond_interface, mutex, abs_timeout);
}
-extern "C" int pthread_cond_timedwait_relative_np(pthread_cond_t* cond, pthread_mutex_t* mutex, const timespec* reltime) {
- atomic_uint* cond_value_ptr = COND_TO_ATOMIC_POINTER(cond);
- return __pthread_cond_timedwait_relative(cond_value_ptr, mutex, reltime);
+extern "C" int pthread_cond_timedwait_relative_np(pthread_cond_t* cond_interface,
+ pthread_mutex_t* mutex,
+ const timespec* rel_timeout) {
+
+ return __pthread_cond_timedwait_relative(__get_internal_cond(cond_interface), mutex, rel_timeout);
}
-extern "C" int pthread_cond_timeout_np(pthread_cond_t* cond, pthread_mutex_t* mutex, unsigned ms) {
+extern "C" int pthread_cond_timeout_np(pthread_cond_t* cond_interface,
+ pthread_mutex_t* mutex, unsigned ms) {
timespec ts;
timespec_from_ms(ts, ms);
- atomic_uint* cond_value_ptr = COND_TO_ATOMIC_POINTER(cond);
- return __pthread_cond_timedwait_relative(cond_value_ptr, mutex, &ts);
+ return pthread_cond_timedwait_relative_np(cond_interface, mutex, &ts);
}
#endif // !defined(__LP64__)
diff --git a/libc/include/pthread.h b/libc/include/pthread.h
index c701e30..b0389e8 100644
--- a/libc/include/pthread.h
+++ b/libc/include/pthread.h
@@ -73,13 +73,14 @@
};
typedef struct {
- unsigned int value;
-#ifdef __LP64__
- char __reserved[44];
+#if defined(__LP64__)
+ char __private[48];
+#else
+ char __private[4];
#endif
} pthread_cond_t;
-#define PTHREAD_COND_INITIALIZER {0 __RESERVED_INITIALIZER}
+#define PTHREAD_COND_INITIALIZER { { 0 } }
typedef long pthread_mutexattr_t;
typedef long pthread_condattr_t;
diff --git a/tests/pthread_test.cpp b/tests/pthread_test.cpp
index c507faa..e1bbc55 100644
--- a/tests/pthread_test.cpp
+++ b/tests/pthread_test.cpp
@@ -875,7 +875,7 @@
}
TEST(pthread, pthread_cond_broadcast__preserves_condattr_flags) {
-#if defined(__BIONIC__) // This tests a bionic implementation detail.
+#if defined(__BIONIC__)
pthread_condattr_t attr;
pthread_condattr_init(&attr);
@@ -888,16 +888,78 @@
ASSERT_EQ(0, pthread_cond_signal(&cond_var));
ASSERT_EQ(0, pthread_cond_broadcast(&cond_var));
- attr = static_cast<pthread_condattr_t>(cond_var.value);
+ attr = static_cast<pthread_condattr_t>(*reinterpret_cast<uint32_t*>(cond_var.__private));
clockid_t clock;
ASSERT_EQ(0, pthread_condattr_getclock(&attr, &clock));
ASSERT_EQ(CLOCK_MONOTONIC, clock);
int pshared;
ASSERT_EQ(0, pthread_condattr_getpshared(&attr, &pshared));
ASSERT_EQ(PTHREAD_PROCESS_SHARED, pshared);
-#else // __BIONIC__
- GTEST_LOG_(INFO) << "This test does nothing.\n";
-#endif // __BIONIC__
+#else // !defined(__BIONIC__)
+ GTEST_LOG_(INFO) << "This tests a bionic implementation detail.\n";
+#endif // !defined(__BIONIC__)
+}
+
+class pthread_CondWakeupTest : public ::testing::Test {
+ protected:
+ pthread_mutex_t mutex;
+ pthread_cond_t cond;
+
+ enum Progress {
+ INITIALIZED,
+ WAITING,
+ SIGNALED,
+ FINISHED,
+ };
+ std::atomic<Progress> progress;
+ pthread_t thread;
+
+ protected:
+ virtual void SetUp() {
+ ASSERT_EQ(0, pthread_mutex_init(&mutex, NULL));
+ ASSERT_EQ(0, pthread_cond_init(&cond, NULL));
+ progress = INITIALIZED;
+ ASSERT_EQ(0,
+ pthread_create(&thread, NULL, reinterpret_cast<void* (*)(void*)>(WaitThreadFn), this));
+ }
+
+ virtual void TearDown() {
+ ASSERT_EQ(0, pthread_join(thread, NULL));
+ ASSERT_EQ(FINISHED, progress);
+ ASSERT_EQ(0, pthread_cond_destroy(&cond));
+ ASSERT_EQ(0, pthread_mutex_destroy(&mutex));
+ }
+
+ void SleepUntilProgress(Progress expected_progress) {
+ while (progress != expected_progress) {
+ usleep(5000);
+ }
+ usleep(5000);
+ }
+
+ private:
+ static void WaitThreadFn(pthread_CondWakeupTest* test) {
+ ASSERT_EQ(0, pthread_mutex_lock(&test->mutex));
+ test->progress = WAITING;
+ while (test->progress == WAITING) {
+ ASSERT_EQ(0, pthread_cond_wait(&test->cond, &test->mutex));
+ }
+ ASSERT_EQ(SIGNALED, test->progress);
+ test->progress = FINISHED;
+ ASSERT_EQ(0, pthread_mutex_unlock(&test->mutex));
+ }
+};
+
+TEST_F(pthread_CondWakeupTest, signal) {
+ SleepUntilProgress(WAITING);
+ progress = SIGNALED;
+ pthread_cond_signal(&cond);
+}
+
+TEST_F(pthread_CondWakeupTest, broadcast) {
+ SleepUntilProgress(WAITING);
+ progress = SIGNALED;
+ pthread_cond_broadcast(&cond);
}
TEST(pthread, pthread_mutex_timedlock) {
