Removing the static initializer in ManagedStatic.cpp by using llvm_call_once to initialize the ManagedStatic mutex.

Summary:
This patch adds an llvm_call_once which is a wrapper around std::call_once on platforms where it is available and devoid of bugs. The patch also migrates the ManagedStatic mutex to be allocated using llvm_call_once.

These changes are philosophically equivalent to the changes added in r219638, which were reverted due to a hang on Win32 which was the result of a bug in the Windows implementation of std::call_once.

Reviewers: aaron.ballman, chapuni, chandlerc, rnk

Reviewed By: rnk

Subscribers: majnemer, llvm-commits

Differential Revision: http://reviews.llvm.org/D5922

llvm-svn: 220932

5 files changed, 44 insertions, 4 deletions

diff --git a/llvm/lib/Support/CMakeLists.txt b/llvm/lib/Support/CMakeLists.txt
index daed4f12e2b..32b96fa379d 100644
--- a/llvm/lib/Support/CMakeLists.txt
+++ b/llvm/lib/Support/CMakeLists.txt
@@ -102,6 +102,7 @@ add_llvm_library(LLVMSupport
   Unix/Program.inc
   Unix/RWMutex.inc
   Unix/Signals.inc
+  Unix/Threading.inc
   Unix/ThreadLocal.inc
   Unix/TimeValue.inc
   Unix/Watchdog.inc
@@ -114,6 +115,7 @@ add_llvm_library(LLVMSupport
   Windows/Program.inc
   Windows/RWMutex.inc
   Windows/Signals.inc
+  Windows/Threading.inc
   Windows/ThreadLocal.inc
   Windows/TimeValue.inc
   Windows/Watchdog.inc
diff --git a/llvm/lib/Support/ManagedStatic.cpp b/llvm/lib/Support/ManagedStatic.cpp
index b8fb2841e52..b1feddc09ec 100644
--- a/llvm/lib/Support/ManagedStatic.cpp
+++ b/llvm/lib/Support/ManagedStatic.cpp
@@ -16,16 +16,23 @@
 #include "llvm/Support/Atomic.h"
 #include "llvm/Support/Mutex.h"
 #include "llvm/Support/MutexGuard.h"
+#include "llvm/Support/Threading.h"
 #include <cassert>
 using namespace llvm;
 
 static const ManagedStaticBase *StaticList = nullptr;
+static sys::Mutex *ManagedStaticMutex = nullptr;
+LLVM_DEFINE_ONCE_FLAG(mutex_init_flag);
 
-static sys::Mutex& getManagedStaticMutex() {
+static void initializeMutex() {
+  ManagedStaticMutex = new sys::Mutex();
+}
+
+static sys::Mutex* getManagedStaticMutex() {
   // We need to use a function local static here, since this can get called
   // during a static constructor and we need to guarantee that it's initialized
   // correctly.
-  static sys::Mutex ManagedStaticMutex;
+  call_once(mutex_init_flag, initializeMutex);
   return ManagedStaticMutex;
 }
 
@@ -33,7 +40,7 @@ void ManagedStaticBase::RegisterManagedStatic(void *(*Creator)(),
                                               void (*Deleter)(void*)) const {
   assert(Creator);
   if (llvm_is_multithreaded()) {
-    MutexGuard Lock(getManagedStaticMutex());
+    MutexGuard Lock(*getManagedStaticMutex());
 
     if (!Ptr) {
       void* tmp = Creator();
@@ -83,7 +90,7 @@ void ManagedStaticBase::destroy() const {
 
 /// llvm_shutdown - Deallocate and destroy all ManagedStatic variables.
 void llvm::llvm_shutdown() {
-  MutexGuard Lock(getManagedStaticMutex());
+  MutexGuard Lock(*getManagedStaticMutex());
 
   while (StaticList)
     StaticList->destroy();
diff --git a/llvm/lib/Support/Threading.cpp b/llvm/lib/Support/Threading.cpp
index ca7f3f64aa3..59b937d9842 100644
--- a/llvm/lib/Support/Threading.cpp
+++ b/llvm/lib/Support/Threading.cpp
@@ -110,3 +110,10 @@ void llvm::llvm_execute_on_thread(void (*Fn)(void*), void *UserData,
 }
 
 #endif
+
+#if defined(LLVM_ON_UNIX)
+#include "Unix/Threading.inc"
+#else
+#include "Windows/Threading.inc"
+#endif
+
diff --git a/llvm/lib/Support/Unix/Threading.inc b/llvm/lib/Support/Unix/Threading.inc
new file mode 100644
index 00000000000..35ec876904a
--- /dev/null
+++ b/llvm/lib/Support/Unix/Threading.inc
@@ -0,0 +1,5 @@
+#include <thread>
+
+void llvm::call_once(once_flag& flag, void (*fptr)(void)) {
+  std::call_once(flag, fptr);
+}
diff --git a/llvm/lib/Support/Windows/Threading.inc b/llvm/lib/Support/Windows/Threading.inc
new file mode 100644
index 00000000000..099c6b28bf6
--- /dev/null
+++ b/llvm/lib/Support/Windows/Threading.inc
@@ -0,0 +1,19 @@
+#include <winbase.h>
+
+void llvm::call_once(once_flag &flag, void (*fptr)(void)) {
+  while (flag != Done) {
+    if (flag == Wait) {
+      ::Sleep(1);
+      continue;
+    }
+
+    sys::cas_flag old_val = sys::CompareAndSwap(&flag, Wait, Uninitialized);
+    if (old_val == Uninitialized) {
+      fptr();
+      sys::MemoryFence();
+      flag = Done;
+      return;
+    }
+  }
+  sys::MemoryFence();
+}