Index: docs/ProgrammersManual.rst =================================================================== --- docs/ProgrammersManual.rst +++ docs/ProgrammersManual.rst @@ -2170,67 +2170,24 @@ using the resultant compiler to build a copy of LLVM with multithreading support. -.. _startmultithreaded: - -Entering and Exiting Multithreaded Mode ---------------------------------------- - -In order to properly protect its internal data structures while avoiding -excessive locking overhead in the single-threaded case, the LLVM must intialize -certain data structures necessary to provide guards around its internals. To do -so, the client program must invoke ``llvm_start_multithreaded()`` before making -any concurrent LLVM API calls. To subsequently tear down these structures, use -the ``llvm_stop_multithreaded()`` call. You can also use the -``llvm_is_multithreaded()`` call to check the status of multithreaded mode. - -Note that both of these calls must be made *in isolation*. That is to say that -no other LLVM API calls may be executing at any time during the execution of -``llvm_start_multithreaded()`` or ``llvm_stop_multithreaded``. It is the -client's responsibility to enforce this isolation. - -The return value of ``llvm_start_multithreaded()`` indicates the success or -failure of the initialization. Failure typically indicates that your copy of -LLVM was built without multithreading support, typically because GCC atomic -intrinsics were not found in your system compiler. In this case, the LLVM API -will not be safe for concurrent calls. However, it *will* be safe for hosting -threaded applications in the JIT, though :ref:`care must be taken -` to ensure that side exits and the like do not accidentally -result in concurrent LLVM API calls. - .. _shutdown: Ending Execution with ``llvm_shutdown()`` ----------------------------------------- When you are done using the LLVM APIs, you should call ``llvm_shutdown()`` to -deallocate memory used for internal structures. This will also invoke -``llvm_stop_multithreaded()`` if LLVM is operating in multithreaded mode. As -such, ``llvm_shutdown()`` requires the same isolation guarantees as -``llvm_stop_multithreaded()``. - -Note that, if you use scope-based shutdown, you can use the -``llvm_shutdown_obj`` class, which calls ``llvm_shutdown()`` in its destructor. - +deallocate memory used for internal structures. .. _managedstatic: Lazy Initialization with ``ManagedStatic`` ------------------------------------------ ``ManagedStatic`` is a utility class in LLVM used to implement static -initialization of static resources, such as the global type tables. Before the -invocation of ``llvm_shutdown()``, it implements a simple lazy initialization -scheme. Once ``llvm_start_multithreaded()`` returns, however, it uses +initialization of static resources, such as the global type tables. In a +single-threaded environment, it implements a simple lazy initialization scheme. +When LLVM is compiled with support for multi-threading, however, it uses double-checked locking to implement thread-safe lazy initialization. -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`` Index: include/llvm-c/Core.h =================================================================== --- include/llvm-c/Core.h +++ include/llvm-c/Core.h @@ -2848,16 +2848,13 @@ * @{ */ -/** 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 */ +/** Deprecated: Multi-threading can only be enabled/disabled with the compile + time define LLVM_ENABLE_THREADS. This function always returns + LLVMIsMultithreaded(). */ LLVMBool LLVMStartMultithreaded(void); -/** 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 */ +/** Deprecated: Multi-threading can only be enabled/disabled with the compile + time define LLVM_ENABLE_THREADS. */ void LLVMStopMultithreaded(void); /** Check whether LLVM is executing in thread-safe mode or not. Index: include/llvm/Support/ManagedStatic.h =================================================================== --- include/llvm/Support/ManagedStatic.h +++ include/llvm/Support/ManagedStatic.h @@ -103,9 +103,6 @@ /// 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(); } }; Index: include/llvm/Support/Mutex.h =================================================================== --- include/llvm/Support/Mutex.h +++ include/llvm/Support/Mutex.h @@ -15,11 +15,13 @@ #define LLVM_SUPPORT_MUTEX_H #include "llvm/Support/Compiler.h" -#include "llvm/Support/Threading.h" #include namespace llvm { + // Forward declare. + bool llvm_is_multithreaded(); + namespace sys { /// @brief Platform agnostic Mutex class. Index: include/llvm/Support/Threading.h =================================================================== --- include/llvm/Support/Threading.h +++ include/llvm/Support/Threading.h @@ -7,40 +7,21 @@ // //===----------------------------------------------------------------------===// // -// TThis file defines llvm_start_multithreaded() and friends. +// This file defines helper functions for running LLVM in a multi-threaded +// environment. // //===----------------------------------------------------------------------===// #ifndef LLVM_SUPPORT_THREADING_H #define LLVM_SUPPORT_THREADING_H -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(); - - /// 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(); +#include "llvm/Support/Mutex.h" - /// llvm_is_multithreaded - Check whether LLVM is executing in thread-safe - /// mode or not. +namespace llvm { + /// llvm_is_multithreaded - returns true if LLVM is compiled with support + /// for multiple threads, and false otherwise. 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. /// Index: lib/IR/Core.cpp =================================================================== --- lib/IR/Core.cpp +++ lib/IR/Core.cpp @@ -2702,11 +2702,10 @@ /*===-- Threading ------------------------------------------------------===*/ LLVMBool LLVMStartMultithreaded() { - return llvm_start_multithreaded(); + return LLVMIsMultithreaded(); } void LLVMStopMultithreaded() { - llvm_stop_multithreaded(); } LLVMBool LLVMIsMultithreaded() { Index: lib/Support/ManagedStatic.cpp =================================================================== --- lib/Support/ManagedStatic.cpp +++ lib/Support/ManagedStatic.cpp @@ -14,17 +14,36 @@ #include "llvm/Support/ManagedStatic.h" #include "llvm/Config/config.h" #include "llvm/Support/Atomic.h" +#include "llvm/Support/MutexGuard.h" #include +#include 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. This also means that we must not "initialize" the +// mutex with nullptr, otherwise it might get reset to nullptr after being +// initialized by std::call_once. +static std::once_flag MutexInitializationFlag; +static std::recursive_mutex *ManagedStaticMutex; + +namespace { + void InitializeManagedStaticMutex() { + std::call_once(MutexInitializationFlag, + []() { ManagedStaticMutex = new std::recursive_mutex(); }); + } +} + void ManagedStaticBase::RegisterManagedStatic(void *(*Creator)(), void (*Deleter)(void*)) const { assert(Creator); if (llvm_is_multithreaded()) { - llvm_acquire_global_lock(); + InitializeManagedStaticMutex(); + std::lock_guard Lock(*ManagedStaticMutex); if (!Ptr) { void* tmp = Creator(); @@ -43,8 +62,6 @@ Next = StaticList; StaticList = this; } - - llvm_release_global_lock(); } else { assert(!Ptr && !DeleterFn && !Next && "Partially initialized ManagedStatic!?"); @@ -75,8 +92,9 @@ /// llvm_shutdown - Deallocate and destroy all ManagedStatic variables. void llvm::llvm_shutdown() { + InitializeManagedStaticMutex(); + std::lock_guard Lock(*ManagedStaticMutex); + while (StaticList) StaticList->destroy(); - - if (llvm_is_multithreaded()) llvm_stop_multithreaded(); } Index: lib/Support/Threading.cpp =================================================================== --- lib/Support/Threading.cpp +++ lib/Support/Threading.cpp @@ -7,7 +7,8 @@ // //===----------------------------------------------------------------------===// // -// This file implements llvm_start_multithreaded() and friends. +// This file implements helper functions for running LLVM in a multi-threaded +// environment. // //===----------------------------------------------------------------------===// @@ -19,50 +20,14 @@ using namespace llvm; -static bool multithreaded_mode = false; - -static sys::Mutex* global_lock = nullptr; - -bool llvm::llvm_start_multithreaded() { +bool llvm::llvm_is_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 Index: lib/Support/Timer.cpp =================================================================== --- lib/Support/Timer.cpp +++ lib/Support/Timer.cpp @@ -18,7 +18,7 @@ #include "llvm/Support/FileSystem.h" #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 +84,13 @@ sys::MemoryFence(); if (tmp) return tmp; - llvm_acquire_global_lock(); + sys::SmartScopedLock Lock(*TimerLock); tmp = DefaultTimerGroup; if (!tmp) { tmp = new TimerGroup("Miscellaneous Ungrouped Timers"); sys::MemoryFence(); DefaultTimerGroup = tmp; } - llvm_release_global_lock(); return tmp; } Index: unittests/Support/ManagedStatic.cpp =================================================================== --- unittests/Support/ManagedStatic.cpp +++ unittests/Support/ManagedStatic.cpp @@ -47,7 +47,6 @@ void *p1 = test1::allocate_stack(a1); void *p2 = test1::allocate_stack(a2); - llvm_start_multithreaded(); pthread_t t1, t2; pthread_create(&t1, &a1, test1::helper, nullptr); pthread_create(&t2, &a2, test1::helper, nullptr); @@ -55,7 +54,6 @@ pthread_join(t2, nullptr); free(p1); free(p2); - llvm_stop_multithreaded(); } #endif