From b4d97b78dfd0d14a788fa3cb876f67a9e666b99b Mon Sep 17 00:00:00 2001
From: Owen Anderson <resistor@mac.com>
Date: Wed, 20 May 2009 00:39:20 +0000
Subject: [PATCH] Add llvm_start_multithreaded(), which starts up the LLVM
 internals in thread-safe mode.  Provide double-check locking initialization
 of ManagedStatic's when running in thread-safe mode.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72151 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/Support/ManagedStatic.h | 44 +++++++++++++++++------
 lib/Support/ManagedStatic.cpp        | 53 +++++++++++++++++++++++-----
 2 files changed, 78 insertions(+), 19 deletions(-)

diff --git a/include/llvm/Support/ManagedStatic.h b/include/llvm/Support/ManagedStatic.h
index d0298e495d3..7eecce3241d 100644
--- a/include/llvm/Support/ManagedStatic.h
+++ b/include/llvm/Support/ManagedStatic.h
@@ -14,8 +14,16 @@
 #ifndef LLVM_SUPPORT_MANAGED_STATIC_H
 #define LLVM_SUPPORT_MANAGED_STATIC_H
 
+#include "llvm/System/Atomic.h"
+
 namespace llvm {
 
+/// object_creator - Helper method for ManagedStatic.
+template<class C>
+void* object_creator() {
+  return new C();
+}
+
 /// object_deleter - Helper method for ManagedStatic.
 ///
 template<class C>
@@ -32,7 +40,7 @@ protected:
   mutable void (*DeleterFn)(void*);
   mutable const ManagedStaticBase *Next;
 
-  void RegisterManagedStatic(void *ObjPtr, void (*deleter)(void*)) const;
+  void RegisterManagedStatic(void *(*creator)(), void (*deleter)(void*)) const;
 public:
   /// isConstructed - Return true if this object has not been created yet.
   bool isConstructed() const { return Ptr != 0; }
@@ -51,25 +59,32 @@ public:
 
   // Accessors.
   C &operator*() {
-    if (!Ptr) LazyInit();
+    void* tmp = Ptr;
+    sys::MemoryFence();
+    if (!tmp) RegisterManagedStatic(object_creator<C>, object_deleter<C>);
+
     return *static_cast<C*>(Ptr);
   }
   C *operator->() {
-    if (!Ptr) LazyInit();
+    void* tmp = Ptr;
+    sys::MemoryFence();
+    if (!tmp) RegisterManagedStatic(object_creator<C>, object_deleter<C>);
+
     return static_cast<C*>(Ptr);
   }
   const C &operator*() const {
-    if (!Ptr) LazyInit();
+    void* tmp = Ptr;
+    sys::MemoryFence();
+    if (!tmp) RegisterManagedStatic(object_creator<C>, object_deleter<C>);
+
     return *static_cast<C*>(Ptr);
   }
   const C *operator->() const {
-    if (!Ptr) LazyInit();
-    return static_cast<C*>(Ptr);
-  }
+    void* tmp = Ptr;
+    sys::MemoryFence();
+    if (!tmp) RegisterManagedStatic(object_creator<C>, object_deleter<C>);
 
-public:
-  void LazyInit() const {
-    RegisterManagedStatic(new C(), object_deleter<C>);
+    return static_cast<C*>(Ptr);
   }
 };
 
@@ -80,6 +95,10 @@ public:
 };
 
 
+/// llvm_start_multithreaded - Allocate and initialize structures needed to
+/// make LLVM safe for multithreading.
+void llvm_start_multithreaded();
+
 /// llvm_shutdown - Deallocate and destroy all ManagedStatic variables.
 void llvm_shutdown();
 
@@ -87,7 +106,10 @@ void llvm_shutdown();
 /// llvm_shutdown_obj - This is a simple helper class that calls
 /// llvm_shutdown() when it is destroyed.
 struct llvm_shutdown_obj {
-  llvm_shutdown_obj() {}
+  llvm_shutdown_obj() { }
+  explicit llvm_shutdown_obj(bool multithreaded) {
+    if (multithreaded) llvm_start_multithreaded();
+  }
   ~llvm_shutdown_obj() { llvm_shutdown(); }
 };
 
diff --git a/lib/Support/ManagedStatic.cpp b/lib/Support/ManagedStatic.cpp
index c365e013c6f..056b6c06c1e 100644
--- a/lib/Support/ManagedStatic.cpp
+++ b/lib/Support/ManagedStatic.cpp
@@ -12,21 +12,44 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/ManagedStatic.h"
+#include "llvm/Config/config.h"
+#include "llvm/System/Atomic.h"
+#include "llvm/System/Mutex.h"
 #include <cassert>
 using namespace llvm;
 
 static const ManagedStaticBase *StaticList = 0;
 
-void ManagedStaticBase::RegisterManagedStatic(void *ObjPtr,
+static sys::Mutex* ManagedStaticMutex = 0;
+
+void ManagedStaticBase::RegisterManagedStatic(void *(*Creator)(),
                                               void (*Deleter)(void*)) const {
-  assert(Ptr == 0 && DeleterFn == 0 && Next == 0 &&
-         "Partially init static?");
-  Ptr = ObjPtr;
-  DeleterFn = Deleter;
+  if (ManagedStaticMutex) {
+    ManagedStaticMutex->acquire();
+
+    if (Ptr == 0) {
+      void* tmp = Creator ? Creator() : 0;
+
+      sys::MemoryFence();
+      Ptr = tmp;
+      DeleterFn = Deleter;
+      
+      // Add to list of managed statics.
+      Next = StaticList;
+      StaticList = this;
+    }
+
+    ManagedStaticMutex->release();
+  } else {
+    assert(Ptr == 0 && DeleterFn == 0 && Next == 0 &&
+	   "Partially initialized ManagedStatic!?");
+    Ptr = Creator ? Creator() : 0;
+    DeleterFn = Deleter;
   
-  // Add to list of managed statics.
-  Next = StaticList;
-  StaticList = this;
+    // Add to list of managed statics.
+    Next = StaticList;
+    StaticList = this;
+  }
 }
 
 void ManagedStaticBase::destroy() const {
@@ -45,9 +68,23 @@ void ManagedStaticBase::destroy() const {
   DeleterFn = 0;
 }
 
+void llvm::llvm_start_multithreaded() {
+#if LLVM_MULTITHREADED
+  assert(ManagedStaticMutex == 0 && "Multithreaded LLVM already initialized!");
+  ManagedStaticMutex = new sys::Mutex(true);
+#else
+  assert(0 && "LLVM built without multithreading support!");
+#endif
+}
+
 /// llvm_shutdown - Deallocate and destroy all ManagedStatic variables.
 void llvm::llvm_shutdown() {
   while (StaticList)
     StaticList->destroy();
+
+  if (ManagedStaticMutex) {
+    delete ManagedStaticMutex;
+    ManagedStaticMutex = 0;
+  }
 }