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Merge "Hide content of pthread_cond_t in pthread_cond_internal_t."

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This commit is contained in:
Yabin Cui
2015-03-16 20:58:01 +00:00
committed by Gerrit Code Review
parent 9923c8cd13 32651b8e8e
commit d3e2a207ff
3 changed files with 150 additions and 79 deletions
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148
libc/bionic/pthread_cond.cpp
View File

@@ -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 @@ int pthread_condattr_destroy(pthread_condattr_t* attr) {
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, const pthread_condattr_t* attr) {
atomic_uint* cond_value_ptr = COND_TO_ATOMIC_POINTER(cond);
unsigned int init_value = 0;
int pthread_cond_init(pthread_cond_t* cond_interface, const pthread_condattr_t* attr) {
pthread_cond_internal_t* cond = __get_internal_cond(cond_interface);
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 @@ static int __pthread_cond_pulse(atomic_uint* cond_value_ptr, int thread_count) {
// 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 @@ int __pthread_cond_timedwait_relative(atomic_uint* cond_value_ptr, pthread_mutex
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__)

9
libc/include/pthread.h
View File

@@ -73,13 +73,14 @@ enum {
};
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;