Cleaned up pthread rwlocks implementation.
- used underscore_style_for_vars
- extracted time related functionality into a function
- cleaned up style
- removed unused fields from pthread_rwlock_t on LP64
- changed reservation in pthread_rwlock_t so that the size of the
structure equals glibc version
Bug: 8133149
Change-Id: I84ad3918678dc7f5e6b3db9b7e9b0899d3abe9cd
diff --git a/libc/bionic/pthread_rwlock.cpp b/libc/bionic/pthread_rwlock.cpp
index b36adcd..3a1b543 100644
--- a/libc/bionic/pthread_rwlock.cpp
+++ b/libc/bionic/pthread_rwlock.cpp
@@ -57,33 +57,39 @@
* should be changed to compare_exchange_strong accompanied by the proper ordering
* constraints (comments have been added with the intending ordering across the code).
*
- * TODO: As it stands now, pendingReaders and pendingWriters could be merged into a
+ * TODO: As it stands now, pending_readers and pending_writers could be merged into a
* a single waiters variable. Keeping them separate adds a bit of clarity and keeps
* the door open for a writer-biased implementation.
*
*/
-#define RWLOCKATTR_DEFAULT 0
-#define RWLOCKATTR_SHARED_MASK 0x0010
+#define RWLOCKATTR_DEFAULT 0
+#define RWLOCKATTR_SHARED_MASK 0x0010
-#define RWLOCK_IS_SHARED(rwlock) ((rwlock)->attr == PTHREAD_PROCESS_SHARED)
+static inline bool rwlock_is_shared(const pthread_rwlock_t* rwlock) {
+ return rwlock->attr == PTHREAD_PROCESS_SHARED;
+}
-extern pthread_internal_t* __get_thread(void);
+static bool timespec_from_absolute(timespec* rel_timeout, const timespec* abs_timeout) {
+ if (abs_timeout != NULL) {
+ if (__timespec_from_absolute(rel_timeout, abs_timeout, CLOCK_REALTIME) < 0) {
+ return false;
+ }
+ }
+ return true;
+}
-int pthread_rwlockattr_init(pthread_rwlockattr_t *attr)
-{
+int pthread_rwlockattr_init(pthread_rwlockattr_t* attr) {
*attr = PTHREAD_PROCESS_PRIVATE;
return 0;
}
-int pthread_rwlockattr_destroy(pthread_rwlockattr_t *attr)
-{
+int pthread_rwlockattr_destroy(pthread_rwlockattr_t* attr) {
*attr = -1;
return 0;
}
-int pthread_rwlockattr_setpshared(pthread_rwlockattr_t *attr, int pshared)
-{
+int pthread_rwlockattr_setpshared(pthread_rwlockattr_t* attr, int pshared) {
switch (pshared) {
case PTHREAD_PROCESS_PRIVATE:
case PTHREAD_PROCESS_SHARED:
@@ -99,9 +105,8 @@
return 0;
}
-int pthread_rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr)
-{
- if (attr) {
+int pthread_rwlock_init(pthread_rwlock_t* rwlock, const pthread_rwlockattr_t* attr) {
+ if (attr != NULL) {
switch (*attr) {
case PTHREAD_PROCESS_SHARED:
case PTHREAD_PROCESS_PRIVATE:
@@ -113,30 +118,30 @@
}
rwlock->state = 0;
- rwlock->pendingReaders = 0;
- rwlock->pendingWriters = 0;
- rwlock->writerThreadId = 0;
+ rwlock->pending_readers = 0;
+ rwlock->pending_writers = 0;
+ rwlock->writer_thread_id = 0;
return 0;
}
-int pthread_rwlock_destroy(pthread_rwlock_t *rwlock)
-{
+int pthread_rwlock_destroy(pthread_rwlock_t* rwlock) {
if (rwlock->state != 0) {
return EBUSY;
}
-
return 0;
}
static int __pthread_rwlock_timedrdlock(pthread_rwlock_t* rwlock, const timespec* abs_timeout) {
- if (__predict_false(__get_thread()->tid == rwlock->writerThreadId)) {
+ if (__predict_false(__get_thread()->tid == rwlock->writer_thread_id)) {
return EDEADLK;
}
+ timespec ts;
+ timespec* rel_timeout = (abs_timeout == NULL) ? NULL : &ts;
bool done = false;
do {
- // This is actually a race read as there's nothing that guarantees the atomicity of integers
+ // This is actually a race read as there's nothing that guarantees the atomicity of integer
// reads / writes. However, in practice this "never" happens so until we switch to C++11 this
// should work fine. The same applies in the other places this idiom is used.
int32_t cur_state = rwlock->state; // C++11 relaxed atomic read
@@ -144,25 +149,18 @@
// Add as an extra reader.
done = __atomic_cmpxchg(cur_state, cur_state + 1, &rwlock->state) == 0; // C++11 memory_order_aquire
} else {
- timespec ts;
- timespec* tsp = NULL;
- if (abs_timeout != NULL) {
- if (__timespec_from_absolute(&ts, abs_timeout, CLOCK_REALTIME) < 0) {
- return ETIMEDOUT;
- }
- tsp = &ts;
+ if (!timespec_from_absolute(rel_timeout, abs_timeout)) {
+ return ETIMEDOUT;
}
// Owner holds it in write mode, hang up.
- // To avoid loosing wake ups the pendingReaders update and the state read should be
+ // To avoid losing wake ups the pending_readers update and the state read should be
// sequentially consistent. (currently enforced by __atomic_inc which creates a full barrier)
- __atomic_inc(&rwlock->pendingReaders); // C++11 memory_order_relaxed (if the futex_wait ensures the ordering)
- if (__futex_wait_ex(&rwlock->state, RWLOCK_IS_SHARED(rwlock), cur_state, tsp) != 0) {
- if (errno == ETIMEDOUT) {
- __atomic_dec(&rwlock->pendingReaders); // C++11 memory_order_relaxed
- return ETIMEDOUT;
- }
+ __atomic_inc(&rwlock->pending_readers); // C++11 memory_order_relaxed (if the futex_wait ensures the ordering)
+ int ret = __futex_wait_ex(&rwlock->state, rwlock_is_shared(rwlock), cur_state, rel_timeout);
+ __atomic_dec(&rwlock->pending_readers); // C++11 memory_order_relaxed
+ if (ret == -ETIMEDOUT) {
+ return ETIMEDOUT;
}
- __atomic_dec(&rwlock->pendingReaders); // C++11 memory_order_relaxed
}
} while (!done);
@@ -171,10 +169,12 @@
static int __pthread_rwlock_timedwrlock(pthread_rwlock_t* rwlock, const timespec* abs_timeout) {
int tid = __get_thread()->tid;
- if (__predict_false(tid == rwlock->writerThreadId)) {
+ if (__predict_false(tid == rwlock->writer_thread_id)) {
return EDEADLK;
}
+ timespec ts;
+ timespec* rel_timeout = (abs_timeout == NULL) ? NULL : &ts;
bool done = false;
do {
int32_t cur_state = rwlock->state;
@@ -182,29 +182,22 @@
// Change state from 0 to -1.
done = __atomic_cmpxchg(0 /* cur_state */, -1 /* new state */, &rwlock->state) == 0; // C++11 memory_order_aquire
} else {
- timespec ts;
- timespec* tsp = NULL;
- if (abs_timeout != NULL) {
- if (__timespec_from_absolute(&ts, abs_timeout, CLOCK_REALTIME) < 0) {
- return ETIMEDOUT;
- }
- tsp = &ts;
+ if (!timespec_from_absolute(rel_timeout, abs_timeout)) {
+ return ETIMEDOUT;
}
// Failed to acquire, hang up.
- // To avoid loosing wake ups the pendingWriters update and the state read should be
+ // To avoid losing wake ups the pending_writers update and the state read should be
// sequentially consistent. (currently enforced by __atomic_inc which creates a full barrier)
- __atomic_inc(&rwlock->pendingWriters); // C++11 memory_order_relaxed (if the futex_wait ensures the ordering)
- if (__futex_wait_ex(&rwlock->state, RWLOCK_IS_SHARED(rwlock), cur_state, tsp) != 0) {
- if (errno == ETIMEDOUT) {
- __atomic_dec(&rwlock->pendingWriters); // C++11 memory_order_relaxed
- return ETIMEDOUT;
- }
+ __atomic_inc(&rwlock->pending_writers); // C++11 memory_order_relaxed (if the futex_wait ensures the ordering)
+ int ret = __futex_wait_ex(&rwlock->state, rwlock_is_shared(rwlock), cur_state, rel_timeout);
+ __atomic_dec(&rwlock->pending_writers); // C++11 memory_order_relaxed
+ if (ret == -ETIMEDOUT) {
+ return ETIMEDOUT;
}
- __atomic_dec(&rwlock->pendingWriters); // C++11 memory_order_relaxed
}
} while (!done);
- rwlock->writerThreadId = tid;
+ rwlock->writer_thread_id = tid;
return 0;
}
@@ -212,8 +205,11 @@
return __pthread_rwlock_timedrdlock(rwlock, NULL);
}
-int pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock)
-{
+int pthread_rwlock_timedrdlock(pthread_rwlock_t* rwlock, const timespec* abs_timeout) {
+ return __pthread_rwlock_timedrdlock(rwlock, abs_timeout);
+}
+
+int pthread_rwlock_tryrdlock(pthread_rwlock_t* rwlock) {
int32_t cur_state = rwlock->state;
if (cur_state >= 0) {
if(__atomic_cmpxchg(cur_state, cur_state + 1, &rwlock->state) != 0) { // C++11 memory_order_acquire
@@ -225,16 +221,15 @@
return 0;
}
-int pthread_rwlock_timedrdlock(pthread_rwlock_t* rwlock, const timespec* abs_timeout) {
- return __pthread_rwlock_timedrdlock(rwlock, abs_timeout);
-}
-
int pthread_rwlock_wrlock(pthread_rwlock_t* rwlock) {
return __pthread_rwlock_timedwrlock(rwlock, NULL);
}
-int pthread_rwlock_trywrlock(pthread_rwlock_t *rwlock)
-{
+int pthread_rwlock_timedwrlock(pthread_rwlock_t* rwlock, const timespec* abs_timeout) {
+ return __pthread_rwlock_timedwrlock(rwlock, abs_timeout);
+}
+
+int pthread_rwlock_trywrlock(pthread_rwlock_t* rwlock) {
int tid = __get_thread()->tid;
int32_t cur_state = rwlock->state;
if (cur_state == 0) {
@@ -245,16 +240,12 @@
return EBUSY;
}
- rwlock->writerThreadId = tid;
+ rwlock->writer_thread_id = tid;
return 0;
}
-int pthread_rwlock_timedwrlock(pthread_rwlock_t* rwlock, const timespec* abs_timeout) {
- return __pthread_rwlock_timedwrlock(rwlock, abs_timeout);
-}
-int pthread_rwlock_unlock(pthread_rwlock_t *rwlock)
-{
+int pthread_rwlock_unlock(pthread_rwlock_t* rwlock) {
int tid = __get_thread()->tid;
bool done = false;
do {
@@ -263,11 +254,11 @@
return EPERM;
}
if (cur_state == -1) {
- if (rwlock->writerThreadId != tid) {
+ if (rwlock->writer_thread_id != tid) {
return EPERM;
}
// We're no longer the owner.
- rwlock->writerThreadId = 0;
+ rwlock->writer_thread_id = 0;
// Change state from -1 to 0.
// We use __atomic_cmpxchg to achieve sequential consistency of the state store and
// the following pendingX loads. A simple store with memory_order_release semantics
@@ -276,8 +267,8 @@
__atomic_cmpxchg(-1 /* cur_state*/, 0 /* new state */, &rwlock->state); // C++11 maybe memory_order_seq_cst?
// Wake any waiters.
- if (__predict_false(rwlock->pendingReaders > 0 || rwlock->pendingWriters > 0)) {
- __futex_wake_ex(&rwlock->state, RWLOCK_IS_SHARED(rwlock), INT_MAX);
+ if (__predict_false(rwlock->pending_readers > 0 || rwlock->pending_writers > 0)) {
+ __futex_wake_ex(&rwlock->state, rwlock_is_shared(rwlock), INT_MAX);
}
done = true;
} else { // cur_state > 0
@@ -286,8 +277,8 @@
done = __atomic_cmpxchg(cur_state, cur_state - 1, &rwlock->state) == 0; // C++11 maybe memory_order_seq_cst?
if (done && (cur_state - 1) == 0) {
// There are no more readers, wake any waiters.
- if (__predict_false(rwlock->pendingReaders > 0 || rwlock->pendingWriters > 0)) {
- __futex_wake_ex(&rwlock->state, RWLOCK_IS_SHARED(rwlock), INT_MAX);
+ if (__predict_false(rwlock->pending_readers > 0 || rwlock->pending_writers > 0)) {
+ __futex_wake_ex(&rwlock->state, rwlock_is_shared(rwlock), INT_MAX);
}
}
}
diff --git a/libc/include/pthread.h b/libc/include/pthread.h
index 346901a..5c9b626 100644
--- a/libc/include/pthread.h
+++ b/libc/include/pthread.h
@@ -94,17 +94,28 @@
typedef long pthread_rwlockattr_t;
typedef struct {
+#if !defined(__LP64__)
pthread_mutex_t __unused_lock;
pthread_cond_t __unused_cond;
+#endif
volatile int32_t state; // 0=unlock, -1=writer lock, +n=reader lock
- volatile int32_t writerThreadId;
- volatile int32_t pendingReaders;
- volatile int32_t pendingWriters;
+ volatile int32_t writer_thread_id;
+ volatile int32_t pending_readers;
+ volatile int32_t pending_writers;
int32_t attr;
- void* __reserved[3];
+#ifdef __LP64__
+ char __reserved[36];
+#else
+ char __reserved[12];
+#endif
+
} pthread_rwlock_t;
-#define PTHREAD_RWLOCK_INITIALIZER { PTHREAD_MUTEX_INITIALIZER, PTHREAD_COND_INITIALIZER, 0, 0, 0, 0, 0, { NULL, NULL, NULL } }
+#ifdef __LP64__
+ #define PTHREAD_RWLOCK_INITIALIZER { 0, 0, 0, 0, 0, { 0 } }
+#else
+ #define PTHREAD_RWLOCK_INITIALIZER { PTHREAD_MUTEX_INITIALIZER, PTHREAD_COND_INITIALIZER, 0, 0, 0, 0, 0, { 0 } }
+#endif
typedef int pthread_key_t;
typedef long pthread_t;