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

llvm-svn: 211277

5 files changed, 22 insertions, 30 deletions

diff --git a/llvm/docs/ProgrammersManual.rst b/llvm/docs/ProgrammersManual.rst
index 4973e5c6671..df3795a34d3 100644
--- a/llvm/docs/ProgrammersManual.rst
+++ b/llvm/docs/ProgrammersManual.rst
@@ -2226,11 +2226,6 @@ Note that, because no other threads are allowed to issue LLVM API calls before
 ``llvm_start_multithreaded()`` returns, it is possible to have
 ``ManagedStatic``\ s of ``llvm::sys::Mutex``\ s.
 
-The ``llvm_acquire_global_lock()`` and ``llvm_release_global_lock`` APIs provide
-access to the global lock used to implement the double-checked locking for lazy
-initialization.  These should only be used internally to LLVM, and only if you
-know what you're doing!
-
 .. _llvmcontext:
 
 Achieving Isolation with ``LLVMContext``
diff --git a/llvm/include/llvm/Support/Threading.h b/llvm/include/llvm/Support/Threading.h
index a7e8774558d..d84d1186795 100644
--- a/llvm/include/llvm/Support/Threading.h
+++ b/llvm/include/llvm/Support/Threading.h
@@ -33,14 +33,6 @@ namespace llvm {
   /// mode or not.
   bool llvm_is_multithreaded();
 
-  /// acquire_global_lock - Acquire the global lock.  This is a no-op if called
-  /// before llvm_start_multithreaded().
-  void llvm_acquire_global_lock();
-
-  /// release_global_lock - Release the global lock.  This is a no-op if called
-  /// before llvm_start_multithreaded().
-  void llvm_release_global_lock();
-
   /// llvm_execute_on_thread - Execute the given \p UserFn on a separate
   /// thread, passing it the provided \p UserData.
   ///
diff --git a/llvm/lib/Support/ManagedStatic.cpp b/llvm/lib/Support/ManagedStatic.cpp
index 6a1c2a545a8..9d7e99f97fb 100644
--- a/llvm/lib/Support/ManagedStatic.cpp
+++ b/llvm/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/llvm/lib/Support/Threading.cpp b/llvm/lib/Support/Threading.cpp
index 1acfa79b11d..2358dde0e6c 100644
--- a/llvm/lib/Support/Threading.cpp
+++ b/llvm/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/llvm/lib/Support/Timer.cpp b/llvm/lib/Support/Timer.cpp
index 61465ae5e8b..210bda754e7 100644
--- a/llvm/lib/Support/Timer.cpp
+++ b/llvm/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;
 }