Merge pull request #1068 from Mathewnd/master

options/posix: fix sys_futex_wait handling and fix an issue in pthread_once

options/internal/generic/threads.cpp

@@ -157,7 +157,8 @@ int thread_mutex_lock(struct __mlibc_mutex *mutex) {
 
 				// If the wait returns EAGAIN, that means that the mutex_waiters_bit was just unset by
 				// some other thread. In this case, we should loop back around.
-				if (e && e != EAGAIN)
+				// Also do so in case of a signal being caught.
+				if (e && e != EAGAIN && e != EINTR)
 					mlibc::panicLogger() << "sys_futex_wait() failed with error code " << e << frg::endlog;
 
 				// Opportunistically try to take the lock after we wake up.

options/internal/include/mlibc/lock.hpp

@@ -50,7 +50,8 @@ struct FutexLockImpl {
 
 					// If the wait returns EAGAIN, that means that the waitersBit was just unset by
 					// some other thread. In this case, we should loop back around.
-					if (e && e != EAGAIN)
+					// Also loop around in case of a signal interrupting the wait
+					if (e && e != EAGAIN && e != EINTR)
 						mlibc::panicLogger() << "sys_futex_wait() failed with error code " << e << frg::endlog;
 
 					// Opportunistically try to take the lock after we wake up.

options/posix/generic/pthread-stubs.cpp

@@ -844,7 +844,10 @@ int pthread_once(pthread_once_t *once, void (*function) (void)) {
 		}else{
 			// a different thread is currently running the initializer.
 			__ensure(expected == onceLocked);
-			if(int e = mlibc::sys_futex_wait((int *)&once->__mlibc_done, onceLocked, nullptr); e)
+			// if the wait gets interrupted by a signal, check again.
+			// EAGAIN will also be a retry, as it means the other thread completed
+			// and changed the __mlibc_done variable to signal it before we actually went to sleep.
+			if(int e = mlibc::sys_futex_wait((int *)&once->__mlibc_done, onceLocked, nullptr); e && e != EINTR && e != EAGAIN)
 				__ensure(!"sys_futex_wait() failed");
 			expected =  __atomic_load_n(&once->__mlibc_done, __ATOMIC_ACQUIRE);
 		}