Fix //aos/common:event
I discovered while using ipc_comparison that it didn't properly handle
spurious wakeups. We don't use it very widely, so it's not surprising
that this bug went unnoticed.
Change-Id: I6675fa2f54ce185d0c67965c2a780ad550978133
diff --git a/aos/common/event.cc b/aos/common/event.cc
index ae32d39..af9c9c5 100644
--- a/aos/common/event.cc
+++ b/aos/common/event.cc
@@ -11,25 +11,28 @@
}
void Event::Wait() {
- int ret;
- do {
- ret = futex_wait(&impl_);
- } while (ret == 1);
- if (ret == 0) return;
- CHECK_EQ(-1, ret);
- PLOG(FATAL, "futex_wait(%p) failed", &impl_);
+ while (__atomic_load_n(&impl_, __ATOMIC_SEQ_CST) == 0) {
+ const int ret = futex_wait(&impl_);
+ if (ret != 0) {
+ CHECK_EQ(-1, ret);
+ PLOG(FATAL, "futex_wait(%p) failed", &impl_);
+ }
+ }
}
bool Event::WaitTimeout(const ::aos::time::Time &timeout) {
const auto timeout_timespec = timeout.ToTimespec();
- int ret;
- do {
- ret = futex_wait_timeout(&impl_, &timeout_timespec);
- } while (ret == 1);
- if (ret == 0) return true;
- if (ret == 2) return false;
- CHECK_EQ(-1, ret);
- PLOG(FATAL, "futex_wait(%p) failed", &impl_);
+ while (true) {
+ if (__atomic_load_n(&impl_, __ATOMIC_SEQ_CST) != 0) {
+ return true;
+ }
+ const int ret = futex_wait_timeout(&impl_, &timeout_timespec);
+ if (ret != 0) {
+ if (ret == 2) return false;
+ CHECK_EQ(-1, ret);
+ PLOG(FATAL, "futex_wait(%p) failed", &impl_);
+ }
+ }
}
// We're not going to expose the number woken because that's not easily portable
diff --git a/aos/linux_code/ipc_lib/aos_sync.cc b/aos/linux_code/ipc_lib/aos_sync.cc
index 92eb1a1..b0b560e 100644
--- a/aos/linux_code/ipc_lib/aos_sync.cc
+++ b/aos/linux_code/ipc_lib/aos_sync.cc
@@ -954,9 +954,6 @@
int futex_wait_timeout(aos_futex *m, const struct timespec *timeout) {
RunObservers run_observers(m, false);
- if (__atomic_load_n(m, __ATOMIC_SEQ_CST) != 0) {
- return 0;
- }
const int ret = sys_futex_wait(FUTEX_WAIT, m, 0, timeout);
if (ret != 0) {
if (ret == -EINTR) {
diff --git a/aos/linux_code/ipc_lib/aos_sync.h b/aos/linux_code/ipc_lib/aos_sync.h
index 3495e73..5b7a865 100644
--- a/aos/linux_code/ipc_lib/aos_sync.h
+++ b/aos/linux_code/ipc_lib/aos_sync.h
@@ -111,9 +111,10 @@
// example messages are available to read on a queue), use the condition_
// functions or there will be race conditions.
-// Wait for the futex to be set. Will return immediately if it's already set.
+// Wait for the futex to be set. Will return immediately if it's already set
+// (after a syscall).
// Returns 0 if successful or it was already set, 1 if interrupted by a signal,
-// or -1 with an error in errno.
+// or -1 with an error in errno. Can return 0 spuriously.
int futex_wait(aos_futex *m) __attribute__((warn_unused_result));
// The same as futex_wait except returns 2 if it times out.
int futex_wait_timeout(aos_futex *m, const struct timespec *timeout)