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-rw-r--r--src/google/protobuf/stubs/once.cc79
1 files changed, 45 insertions, 34 deletions
diff --git a/src/google/protobuf/stubs/once.cc b/src/google/protobuf/stubs/once.cc
index 5b7af9c..1e24b85 100644
--- a/src/google/protobuf/stubs/once.cc
+++ b/src/google/protobuf/stubs/once.cc
@@ -35,54 +35,65 @@
// This header is intended to be included only by internal .cc files and
// generated .pb.cc files. Users should not use this directly.
+#include <google/protobuf/stubs/once.h>
+
+#ifndef GOOGLE_PROTOBUF_NO_THREAD_SAFETY
+
#ifdef _WIN32
#include <windows.h>
+#else
+#include <sched.h>
#endif
-#include <google/protobuf/stubs/once.h>
+#include <google/protobuf/stubs/atomicops.h>
namespace google {
namespace protobuf {
-#ifdef _WIN32
-
-struct ProtobufOnceInternal {
- ProtobufOnceInternal() {
- InitializeCriticalSection(&critical_section);
- }
- ~ProtobufOnceInternal() {
- DeleteCriticalSection(&critical_section);
- }
- CRITICAL_SECTION critical_section;
-};
-
-ProtobufOnceType::~ProtobufOnceType()
-{
- delete internal_;
- internal_ = NULL;
-}
+namespace {
-ProtobufOnceType::ProtobufOnceType() {
- // internal_ may be non-NULL if Init() was already called.
- if (internal_ == NULL) internal_ = new ProtobufOnceInternal;
+void SchedYield() {
+#ifdef _WIN32
+ Sleep(0);
+#else // POSIX
+ sched_yield();
+#endif
}
-void ProtobufOnceType::Init(void (*init_func)()) {
- // internal_ may be NULL if we're still in dynamic initialization and the
- // constructor has not been called yet. As mentioned in once.h, we assume
- // that the program is still single-threaded at this time, and therefore it
- // should be safe to initialize internal_ like so.
- if (internal_ == NULL) internal_ = new ProtobufOnceInternal;
+} // namespace
- EnterCriticalSection(&internal_->critical_section);
- if (!initialized_) {
- init_func();
- initialized_ = true;
+void GoogleOnceInitImpl(ProtobufOnceType* once, Closure* closure) {
+ internal::AtomicWord state = internal::Acquire_Load(once);
+ // Fast path. The provided closure was already executed.
+ if (state == ONCE_STATE_DONE) {
+ return;
+ }
+ // The closure execution did not complete yet. The once object can be in one
+ // of the two following states:
+ // - UNINITIALIZED: We are the first thread calling this function.
+ // - EXECUTING_CLOSURE: Another thread is already executing the closure.
+ //
+ // First, try to change the state from UNINITIALIZED to EXECUTING_CLOSURE
+ // atomically.
+ state = internal::Acquire_CompareAndSwap(
+ once, ONCE_STATE_UNINITIALIZED, ONCE_STATE_EXECUTING_CLOSURE);
+ if (state == ONCE_STATE_UNINITIALIZED) {
+ // We are the first thread to call this function, so we have to call the
+ // closure.
+ closure->Run();
+ internal::Release_Store(once, ONCE_STATE_DONE);
+ } else {
+ // Another thread has already started executing the closure. We need to
+ // wait until it completes the initialization.
+ while (state == ONCE_STATE_EXECUTING_CLOSURE) {
+ // Note that futex() could be used here on Linux as an improvement.
+ SchedYield();
+ state = internal::Acquire_Load(once);
+ }
}
- LeaveCriticalSection(&internal_->critical_section);
}
-#endif
-
} // namespace protobuf
} // namespace google
+
+#endif // GOOGLE_PROTOBUF_NO_THREAD_SAFETY