Revert "Remove support for runtime multi-threading."

This reverts revision r210600.

llvm-svn: 210603

include/llvm-c/Core.h

@@ -2848,13 +2848,16 @@ void LLVMDisposePassManager(LLVMPassManagerRef PM);
  * @{
  */
 
-/** Deprecated: Multi-threading can only be enabled/disabled with the compile
-    time define LLVM_ENABLE_THREADS.  This function always returns
-    LLVMIsMultithreaded(). */
+/** Allocate and initialize structures needed to make LLVM safe for
+    multithreading. The return value indicates whether multithreaded
+    initialization succeeded. Must be executed in isolation from all
+    other LLVM api calls.
+    @see llvm::llvm_start_multithreaded */
 LLVMBool LLVMStartMultithreaded(void);
 
-/** Deprecated: Multi-threading can only be enabled/disabled with the compile
-    time define LLVM_ENABLE_THREADS. */
+/** Deallocate structures necessary to make LLVM safe for multithreading.
+    Must be executed in isolation from all other LLVM api calls.
+    @see llvm::llvm_stop_multithreaded */
 void LLVMStopMultithreaded(void);
 
 /** Check whether LLVM is executing in thread-safe mode or not.

include/llvm/Support/ManagedStatic.h

@@ -103,6 +103,9 @@ void llvm_shutdown();
 /// llvm_shutdown() when it is destroyed.
 struct llvm_shutdown_obj {
   llvm_shutdown_obj() { }
+  explicit llvm_shutdown_obj(bool multithreaded) {
+    if (multithreaded) llvm_start_multithreaded();
+  }
   ~llvm_shutdown_obj() { llvm_shutdown(); }
 };
 

include/llvm/Support/Threading.h

@@ -14,33 +14,33 @@
 #ifndef LLVM_SUPPORT_THREADING_H
 #define LLVM_SUPPORT_THREADING_H
 
-#include "llvm/Config/llvm-config.h"
-#include "llvm/Support/Compiler.h"
-#include <mutex>
-
 namespace llvm {
+  /// llvm_start_multithreaded - Allocate and initialize structures needed to
+  /// make LLVM safe for multithreading.  The return value indicates whether
+  /// multithreaded initialization succeeded.  LLVM will still be operational
+  /// on "failed" return, and will still be safe for hosting threading
+  /// applications in the JIT, but will not be safe for concurrent calls to the
+  /// LLVM APIs.
+  /// THIS MUST EXECUTE IN ISOLATION FROM ALL OTHER LLVM API CALLS.
+  bool llvm_start_multithreaded();
 
-#if LLVM_ENABLE_THREADS != 0
-  typedef std::mutex mutex;
-  typedef std::recursive_mutex recursive_mutex;
-#else
-  class null_mutex {
-  public:
-    void lock() { }
-    void unlock() { }
-    bool try_lock() { return true; }
-  };
-  typedef null_mutex mutex;
-  typedef null_mutex recursive_mutex;
-#endif
+  /// llvm_stop_multithreaded - Deallocate structures necessary to make LLVM
+  /// safe for multithreading.
+  /// THIS MUST EXECUTE IN ISOLATION FROM ALL OTHER LLVM API CALLS.
+  void llvm_stop_multithreaded();
 
-  /// llvm_get_global_lock() - returns the llvm global lock object.
-  llvm::recursive_mutex &llvm_get_global_lock();
-
-  /// llvm_is_multithreaded() - returns true if LLVM is compiled with support
-  /// for multiple threads, and false otherwise.
+  /// llvm_is_multithreaded - Check whether LLVM is executing in thread-safe
+  /// 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.
   ///

lib/IR/Core.cpp

@@ -2702,10 +2702,11 @@ void LLVMDisposePassManager(LLVMPassManagerRef PM) {
 /*===-- Threading ------------------------------------------------------===*/
 
 LLVMBool LLVMStartMultithreaded() {
-  return LLVMIsMultithreaded();
+  return llvm_start_multithreaded();
 }
 
 void LLVMStopMultithreaded() {
+  llvm_stop_multithreaded();
 }
 
 LLVMBool LLVMIsMultithreaded() {

lib/Support/ErrorHandling.cpp

@@ -23,7 +23,6 @@
 #include "llvm/Support/raw_ostream.h"
 #include <cassert>
 #include <cstdlib>
-#include <mutex>
 
 #if defined(HAVE_UNISTD_H)
 # include <unistd.h>
@@ -38,18 +37,16 @@ using namespace llvm;
 static fatal_error_handler_t ErrorHandler = nullptr;
 static void *ErrorHandlerUserData = nullptr;
 
-static llvm::recursive_mutex ErrorHandlerMutex;
-
 void llvm::install_fatal_error_handler(fatal_error_handler_t handler,
                                        void *user_data) {
-  std::lock_guard<llvm::recursive_mutex> Lock(ErrorHandlerMutex);
+  assert(!llvm_is_multithreaded() &&
+         "Cannot register error handlers after starting multithreaded mode!\n");
   assert(!ErrorHandler && "Error handler already registered!\n");
   ErrorHandler = handler;
   ErrorHandlerUserData = user_data;
 }
 
 void llvm::remove_fatal_error_handler() {
-  std::lock_guard<llvm::recursive_mutex> Lock(ErrorHandlerMutex);
   ErrorHandler = nullptr;
 }
 
@@ -66,7 +63,6 @@ void llvm::report_fatal_error(StringRef Reason, bool GenCrashDiag) {
 }
 
 void llvm::report_fatal_error(const Twine &Reason, bool GenCrashDiag) {
-  std::lock_guard<llvm::recursive_mutex> Lock(ErrorHandlerMutex);
   if (ErrorHandler) {
     ErrorHandler(ErrorHandlerUserData, Reason.str(), GenCrashDiag);
   } else {

lib/Support/ManagedStatic.cpp

@@ -15,7 +15,6 @@
 #include "llvm/Config/config.h"
 #include "llvm/Support/Atomic.h"
 #include <cassert>
-#include <mutex>
 using namespace llvm;
 
 static const ManagedStaticBase *StaticList = nullptr;
@@ -24,7 +23,7 @@ void ManagedStaticBase::RegisterManagedStatic(void *(*Creator)(),
                                               void (*Deleter)(void*)) const {
   assert(Creator);
   if (llvm_is_multithreaded()) {
-    std::lock_guard<llvm::recursive_mutex> Lock(llvm_get_global_lock());
+    llvm_acquire_global_lock();
 
     if (!Ptr) {
       void* tmp = Creator();
@@ -45,6 +44,7 @@ void ManagedStaticBase::RegisterManagedStatic(void *(*Creator)(),
       StaticList = this;
     }
 
+    llvm_release_global_lock();
   } else {
     assert(!Ptr && !DeleterFn && !Next &&
            "Partially initialized ManagedStatic!?");
@@ -77,4 +77,6 @@ void ManagedStaticBase::destroy() const {
 void llvm::llvm_shutdown() {
   while (StaticList)
     StaticList->destroy();
+
+  if (llvm_is_multithreaded()) llvm_stop_multithreaded();
 }

lib/Support/Threading.cpp

@@ -19,19 +19,50 @@
 
 using namespace llvm;
 
-llvm::recursive_mutex& llvm::llvm_get_global_lock() {
-  static llvm::recursive_mutex global_lock;
-  return global_lock;
-}
+static bool multithreaded_mode = false;
 
-bool llvm::llvm_is_multithreaded() {
+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().
+  sys::MemoryFence();
   return true;
 #else
   return false;
 #endif
 }
 
+void llvm::llvm_stop_multithreaded() {
+#if LLVM_ENABLE_THREADS != 0
+  assert(multithreaded_mode && "Not currently multithreaded!");
+
+  // We fence here to insure that all threaded operations are complete BEFORE we
+  // return from llvm_stop_multithreaded().
+  sys::MemoryFence();
+
+  multithreaded_mode = false;
+  delete global_lock;
+#endif
+}
+
+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>
 

lib/Support/Timer.cpp

@@ -84,13 +84,14 @@ static TimerGroup *getDefaultTimerGroup() {
   sys::MemoryFence();
   if (tmp) return tmp;
   
-  std::lock_guard<llvm::recursive_mutex> Lock(llvm::llvm_get_global_lock());
+  llvm_acquire_global_lock();
   tmp = DefaultTimerGroup;
   if (!tmp) {
     tmp = new TimerGroup("Miscellaneous Ungrouped Timers");
     sys::MemoryFence();
     DefaultTimerGroup = tmp;
   }
+  llvm_release_global_lock();
 
   return tmp;
 }