From 761f33167f2ae180dddcf48abcfcc3ead0c2d219 Mon Sep 17 00:00:00 2001
From: Zachary Turner <zturner@google.com>
Date: Thu, 19 Jun 2014 16:17:42 +0000
Subject: Kill the LLVM global lock.

This patch removes the LLVM global lock, and updates all existing
users of the global lock to use their own mutex.    None of the
existing users of the global lock were protecting code that was
mutually exclusive with any of the other users of the global
lock, so its purpose was not being met.

Reviewed by: rnk

Differential Revision: http://reviews.llvm.org/D4142

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211277 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Support/ManagedStatic.cpp | 23 ++++++++++++++++++++---
 lib/Support/Threading.cpp     | 12 ------------
 lib/Support/Timer.cpp         |  4 ++--
 3 files changed, 22 insertions(+), 17 deletions(-)

(limited to 'lib/Support')

diff --git a/lib/Support/ManagedStatic.cpp b/lib/Support/ManagedStatic.cpp
index 6a1c2a545a..9d7e99f97f 100644
--- a/lib/Support/ManagedStatic.cpp
+++ b/lib/Support/ManagedStatic.cpp
@@ -15,15 +15,32 @@
 #include "llvm/Config/config.h"
 #include "llvm/Support/Atomic.h"
 #include <cassert>
+#include <mutex>
 using namespace llvm;
 
 static const ManagedStaticBase *StaticList = nullptr;
 
+// ManagedStatics can get created during execution of static constructors.  As a
+// result, we cannot use a global static std::mutex object for the lock since it
+// may not have been constructed.  Instead, we do a call-once initialization of
+// a pointer to a mutex.
+static std::once_flag MutexInitializationFlag;
+static std::recursive_mutex* ManagedStaticMutex = nullptr;
+
+// Not all supported platforms (in particular VS2012) have thread-safe function
+// static initialization, so roll our own.
+static std::recursive_mutex& GetManagedStaticMutex() {
+  std::call_once(MutexInitializationFlag,
+      []() { ManagedStaticMutex = new std::recursive_mutex(); } );
+
+  return *ManagedStaticMutex;
+}
+
 void ManagedStaticBase::RegisterManagedStatic(void *(*Creator)(),
                                               void (*Deleter)(void*)) const {
   assert(Creator);
   if (llvm_is_multithreaded()) {
-    llvm_acquire_global_lock();
+    std::lock_guard<std::recursive_mutex> Lock(GetManagedStaticMutex());
 
     if (!Ptr) {
       void* tmp = Creator();
@@ -43,8 +60,6 @@ void ManagedStaticBase::RegisterManagedStatic(void *(*Creator)(),
       Next = StaticList;
       StaticList = this;
     }
-
-    llvm_release_global_lock();
   } else {
     assert(!Ptr && !DeleterFn && !Next &&
            "Partially initialized ManagedStatic!?");
@@ -75,6 +90,8 @@ void ManagedStaticBase::destroy() const {
 
 /// llvm_shutdown - Deallocate and destroy all ManagedStatic variables.
 void llvm::llvm_shutdown() {
+  std::lock_guard<std::recursive_mutex> Lock(GetManagedStaticMutex());
+
   while (StaticList)
     StaticList->destroy();
 
diff --git a/lib/Support/Threading.cpp b/lib/Support/Threading.cpp
index 1acfa79b11..2358dde0e6 100644
--- a/lib/Support/Threading.cpp
+++ b/lib/Support/Threading.cpp
@@ -21,13 +21,10 @@ using namespace llvm;
 
 static bool multithreaded_mode = false;
 
-static sys::Mutex* global_lock = nullptr;
-
 bool llvm::llvm_start_multithreaded() {
 #if LLVM_ENABLE_THREADS != 0
   assert(!multithreaded_mode && "Already multithreaded!");
   multithreaded_mode = true;
-  global_lock = new sys::Mutex(true);
 
   // We fence here to ensure that all initialization is complete BEFORE we
   // return from llvm_start_multithreaded().
@@ -47,7 +44,6 @@ void llvm::llvm_stop_multithreaded() {
   sys::MemoryFence();
 
   multithreaded_mode = false;
-  delete global_lock;
 #endif
 }
 
@@ -55,14 +51,6 @@ bool llvm::llvm_is_multithreaded() {
   return multithreaded_mode;
 }
 
-void llvm::llvm_acquire_global_lock() {
-  if (multithreaded_mode) global_lock->acquire();
-}
-
-void llvm::llvm_release_global_lock() {
-  if (multithreaded_mode) global_lock->release();
-}
-
 #if LLVM_ENABLE_THREADS != 0 && defined(HAVE_PTHREAD_H)
 #include <pthread.h>
 
diff --git a/lib/Support/Timer.cpp b/lib/Support/Timer.cpp
index 61465ae5e8..210bda754e 100644
--- a/lib/Support/Timer.cpp
+++ b/lib/Support/Timer.cpp
@@ -19,6 +19,7 @@
 #include "llvm/Support/Format.h"
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/Mutex.h"
+#include "llvm/Support/MutexGuard.h"
 #include "llvm/Support/Process.h"
 #include "llvm/Support/raw_ostream.h"
 using namespace llvm;
@@ -84,14 +85,13 @@ static TimerGroup *getDefaultTimerGroup() {
   sys::MemoryFence();
   if (tmp) return tmp;
   
-  llvm_acquire_global_lock();
+  sys::SmartScopedLock<true> Lock(*TimerLock);
   tmp = DefaultTimerGroup;
   if (!tmp) {
     tmp = new TimerGroup("Miscellaneous Ungrouped Timers");
     sys::MemoryFence();
     DefaultTimerGroup = tmp;
   }
-  llvm_release_global_lock();
 
   return tmp;
 }
-- 
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