Merge "Modify MIPS64 stat structure to match a generic one in AOSP."
diff --git a/libc/bionic/pthread_once.cpp b/libc/bionic/pthread_once.cpp
index 6d9d7d1..7688a23 100644
--- a/libc/bionic/pthread_once.cpp
+++ b/libc/bionic/pthread_once.cpp
@@ -27,74 +27,59 @@
*/
#include <pthread.h>
+#include <stdatomic.h>
-#include "private/bionic_atomic_inline.h"
#include "private/bionic_futex.h"
-#define ONCE_INITIALIZING (1 << 0)
-#define ONCE_COMPLETED (1 << 1)
+#define ONCE_INITIALIZATION_NOT_YET_STARTED 0
+#define ONCE_INITIALIZATION_UNDERWAY 1
+#define ONCE_INITIALIZATION_COMPLETE 2
/* NOTE: this implementation doesn't support a init function that throws a C++ exception
* or calls fork()
*/
int pthread_once(pthread_once_t* once_control, void (*init_routine)(void)) {
- volatile pthread_once_t* once_control_ptr = once_control;
+ static_assert(sizeof(atomic_int) == sizeof(pthread_once_t),
+ "pthread_once_t should actually be atomic_int in implementation.");
- // PTHREAD_ONCE_INIT is 0, we use the following bit flags
- // bit 0 set -> initialization is under way
- // bit 1 set -> initialization is complete
+ // We prefer casting to atomic_int instead of declaring pthread_once_t to be atomic_int directly.
+ // Because using the second method pollutes pthread.h, and causes an error when compiling libcxx.
+ atomic_int* once_control_ptr = reinterpret_cast<atomic_int*>(once_control);
// First check if the once is already initialized. This will be the common
// case and we want to make this as fast as possible. Note that this still
// requires a load_acquire operation here to ensure that all the
// stores performed by the initialization function are observable on
// this CPU after we exit.
- if (__predict_true((*once_control_ptr & ONCE_COMPLETED) != 0)) {
- ANDROID_MEMBAR_FULL();
- return 0;
- }
+ int old_value = atomic_load_explicit(once_control_ptr, memory_order_acquire);
while (true) {
- // Try to atomically set the INITIALIZING flag.
- // This requires a cmpxchg loop, and we may need
- // to exit prematurely if we detect that
- // COMPLETED is now set.
- int32_t old_value, new_value;
-
- do {
- old_value = *once_control_ptr;
- if ((old_value & ONCE_COMPLETED) != 0) {
- break;
- }
-
- new_value = old_value | ONCE_INITIALIZING;
- } while (__bionic_cmpxchg(old_value, new_value, once_control_ptr) != 0);
-
- if ((old_value & ONCE_COMPLETED) != 0) {
- // We detected that COMPLETED was set while in our loop.
- ANDROID_MEMBAR_FULL();
+ if (__predict_true(old_value == ONCE_INITIALIZATION_COMPLETE)) {
return 0;
}
- if ((old_value & ONCE_INITIALIZING) == 0) {
- // We got there first, we can jump out of the loop to handle the initialization.
- break;
+ // Try to atomically set the initialization underway flag. This requires a compare exchange
+ // in a loop, and we may need to exit prematurely if the initialization is complete.
+ if (!atomic_compare_exchange_weak_explicit(once_control_ptr, &old_value,
+ ONCE_INITIALIZATION_UNDERWAY,
+ memory_order_acquire, memory_order_acquire)) {
+ continue;
}
- // Another thread is running the initialization and hasn't completed
- // yet, so wait for it, then try again.
+ if (old_value == ONCE_INITIALIZATION_NOT_YET_STARTED) {
+ // We got here first, we can handle the initialization.
+ (*init_routine)();
+
+ // Do a store_release indicating that initialization is complete.
+ atomic_store_explicit(once_control_ptr, ONCE_INITIALIZATION_COMPLETE, memory_order_release);
+
+ // Wake up any waiters, if any.
+ __futex_wake_ex(once_control_ptr, 0, INT_MAX);
+ return 0;
+ }
+
+ // The initialization is underway, wait for its finish.
__futex_wait_ex(once_control_ptr, 0, old_value, NULL);
+ old_value = atomic_load_explicit(once_control_ptr, memory_order_acquire);
}
-
- // Call the initialization function.
- (*init_routine)();
-
- // Do a store_release indicating that initialization is complete.
- ANDROID_MEMBAR_FULL();
- *once_control_ptr = ONCE_COMPLETED;
-
- // Wake up any waiters, if any.
- __futex_wake_ex(once_control_ptr, 0, INT_MAX);
-
- return 0;
}
diff --git a/libc/include/pthread.h b/libc/include/pthread.h
index 2178789..4281132 100644
--- a/libc/include/pthread.h
+++ b/libc/include/pthread.h
@@ -112,7 +112,7 @@
typedef int pthread_key_t;
-typedef volatile int pthread_once_t;
+typedef int pthread_once_t;
#define PTHREAD_ONCE_INIT 0