Use swift_once instead of C++ static initializers

Author: Julian Lettner

stdlib/public/Concurrency/Task.cpp

@@ -92,8 +92,6 @@ void AsyncTask::completeFuture(AsyncContext *context, ExecutorRef executor) {
   using Status = FutureFragment::Status;
   using WaitQueueItem = FutureFragment::WaitQueueItem;
 
-  _swift_tsan_release(static_cast<Job *>(this));
-
   assert(isFuture());
   auto fragment = futureFragment();
 
@@ -105,6 +103,8 @@ void AsyncTask::completeFuture(AsyncContext *context, ExecutorRef executor) {
     hadErrorResult = true;
   }
 
+  _swift_tsan_release(static_cast<Job *>(this));
+
   // Update the status to signal completion.
   auto newQueueHead = WaitQueueItem::get(
     hadErrorResult ? Status::Error : Status::Success,
@@ -125,8 +125,6 @@ void AsyncTask::completeFuture(AsyncContext *context, ExecutorRef executor) {
   // Schedule every waiting task on the executor.
   auto waitingTask = queueHead.getTask();
   while (waitingTask) {
-    _swift_tsan_acquire(static_cast<Job *>(waitingTask));
-
     // Find the next waiting task before we invalidate it by resuming
     // the task.
     auto nextWaitingTask = waitingTask->getNextWaitingTask();
@@ -140,6 +138,8 @@ void AsyncTask::completeFuture(AsyncContext *context, ExecutorRef executor) {
       waitingContext->fillWithSuccess(fragment);
     }
 
+    _swift_tsan_acquire(static_cast<Job *>(waitingTask));
+
     // Enqueue the waiter on the global executor.
     // TODO: allow waiters to fill in a suggested executor
     swift_task_enqueueGlobal(waitingTask);

stdlib/public/Concurrency/ThreadSanitizer.cpp

@@ -23,28 +23,35 @@
 #include <dlfcn.h>
 #endif
 
+namespace {
 using TSanFunc = void(void *);
+TSanFunc *tsan_acquire, *tsan_release;
 
-namespace {
-static TSanFunc *loadSymbol(const char *name) {
+TSanFunc *loadSymbol(const char *name) {
 #if defined(_WIN32)
   return (TSanFunc *)GetProcAddress(GetModuleHandle(NULL), name);
 #else
   return (TSanFunc *)dlsym(RTLD_DEFAULT, name);
 #endif
 }
+
+swift::swift_once_t initOnceToken;
+void initializeThreadSanitizer(void *unused) {
+  tsan_acquire = loadSymbol("__tsan_acquire");
+  tsan_release = loadSymbol("__tsan_release");
 }
+} // anonymous namespace
 
 void swift::_swift_tsan_acquire(void *addr) {
-  static auto ptr = loadSymbol("__tsan_acquire");
-  if (ptr) {
-    ptr(addr);
+  swift_once(&initOnceToken, initializeThreadSanitizer, nullptr);
+  if (tsan_acquire) {
+    tsan_acquire(addr);
   }
 }
 
 void swift::_swift_tsan_release(void *addr) {
-  static auto ptr = loadSymbol("__tsan_release");
-  if (ptr) {
-    ptr(addr);
+  swift_once(&initOnceToken, initializeThreadSanitizer, nullptr);
+  if (tsan_release) {
+    tsan_release(addr);
   }
 }