From c472800bdeec71c89c37ccb7f4799744109343fe Mon Sep 17 00:00:00 2001 From: Zachary Turner Date: Mon, 16 Jun 2014 22:49:41 +0000 Subject: [PATCH] Revert r211066, 211067, 211068, 211069, 211070. These were committed accidentally from the wrong branch before having a review sign-off. llvm-svn: 211072 --- docs/ProgrammersManual.rst | 51 +++++++++++++++++++++++++--- include/llvm-c/Core.h | 13 ++++--- include/llvm/Support/ManagedStatic.h | 3 ++ include/llvm/Support/Mutex.h | 4 +-- include/llvm/Support/Threading.h | 31 +++++++++++++---- lib/IR/Core.cpp | 3 +- lib/Support/ManagedStatic.cpp | 28 +++------------ lib/Support/Threading.cpp | 41 ++++++++++++++++++++-- lib/Support/Timer.cpp | 5 +-- unittests/Support/ManagedStatic.cpp | 2 ++ 10 files changed, 134 insertions(+), 47 deletions(-) diff --git a/docs/ProgrammersManual.rst b/docs/ProgrammersManual.rst index b35364d06a8..4973e5c6671 100644 --- a/docs/ProgrammersManual.rst +++ b/docs/ProgrammersManual.rst @@ -2170,24 +2170,67 @@ compiler, consider compiling LLVM and LLVM-GCC in single-threaded mode, and 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. +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. + .. _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. In a -single-threaded environment, it implements a simple lazy initialization scheme. -When LLVM is compiled with support for multi-threading, however, it uses +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 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`` diff --git a/include/llvm-c/Core.h b/include/llvm-c/Core.h index 8693a3020ab..0e78ed71fa9 100644 --- a/include/llvm-c/Core.h +++ b/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. diff --git a/include/llvm/Support/ManagedStatic.h b/include/llvm/Support/ManagedStatic.h index d8fbfeb8e20..1bb8cea092f 100644 --- a/include/llvm/Support/ManagedStatic.h +++ b/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(); } }; diff --git a/include/llvm/Support/Mutex.h b/include/llvm/Support/Mutex.h index 2f3201a2011..496a4381f3f 100644 --- a/include/llvm/Support/Mutex.h +++ b/include/llvm/Support/Mutex.h @@ -15,13 +15,11 @@ #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. diff --git a/include/llvm/Support/Threading.h b/include/llvm/Support/Threading.h index 8f87cbc7f41..a7e8774558d 100644 --- a/include/llvm/Support/Threading.h +++ b/include/llvm/Support/Threading.h @@ -7,21 +7,40 @@ // //===----------------------------------------------------------------------===// // -// This file defines helper functions for running LLVM in a multi-threaded -// environment. +// TThis file defines llvm_start_multithreaded() and friends. // //===----------------------------------------------------------------------===// #ifndef LLVM_SUPPORT_THREADING_H #define LLVM_SUPPORT_THREADING_H -#include "llvm/Support/Mutex.h" - namespace llvm { - /// llvm_is_multithreaded - returns true if LLVM is compiled with support - /// for multiple threads, and false otherwise. + /// 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(); + + /// 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. /// diff --git a/lib/IR/Core.cpp b/lib/IR/Core.cpp index 68b9baa2baa..197b6cb9054 100644 --- a/lib/IR/Core.cpp +++ b/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() { diff --git a/lib/Support/ManagedStatic.cpp b/lib/Support/ManagedStatic.cpp index ced2b13b3a1..6a1c2a545a8 100644 --- a/lib/Support/ManagedStatic.cpp +++ b/lib/Support/ManagedStatic.cpp @@ -14,36 +14,17 @@ #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()) { - InitializeManagedStaticMutex(); + llvm_acquire_global_lock(); - std::lock_guard Lock(*ManagedStaticMutex); if (!Ptr) { void* tmp = Creator(); @@ -62,6 +43,8 @@ void ManagedStaticBase::RegisterManagedStatic(void *(*Creator)(), Next = StaticList; StaticList = this; } + + llvm_release_global_lock(); } else { assert(!Ptr && !DeleterFn && !Next && "Partially initialized ManagedStatic!?"); @@ -92,9 +75,8 @@ void ManagedStaticBase::destroy() const { /// 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(); } diff --git a/lib/Support/Threading.cpp b/lib/Support/Threading.cpp index 838a71b789d..1acfa79b11d 100644 --- a/lib/Support/Threading.cpp +++ b/lib/Support/Threading.cpp @@ -7,8 +7,7 @@ // //===----------------------------------------------------------------------===// // -// This file implements helper functions for running LLVM in a multi-threaded -// environment. +// This file implements llvm_start_multithreaded() and friends. // //===----------------------------------------------------------------------===// @@ -20,14 +19,50 @@ using namespace llvm; -bool llvm::llvm_is_multithreaded() { +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(). + 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 diff --git a/lib/Support/Timer.cpp b/lib/Support/Timer.cpp index 7738283bad0..61465ae5e8b 100644 --- a/lib/Support/Timer.cpp +++ b/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/MutexGuard.h" +#include "llvm/Support/Mutex.h" #include "llvm/Support/Process.h" #include "llvm/Support/raw_ostream.h" using namespace llvm; @@ -84,13 +84,14 @@ static TimerGroup *getDefaultTimerGroup() { sys::MemoryFence(); if (tmp) return tmp; - sys::SmartScopedLock Lock(*TimerLock); + llvm_acquire_global_lock(); tmp = DefaultTimerGroup; if (!tmp) { tmp = new TimerGroup("Miscellaneous Ungrouped Timers"); sys::MemoryFence(); DefaultTimerGroup = tmp; } + llvm_release_global_lock(); return tmp; } diff --git a/unittests/Support/ManagedStatic.cpp b/unittests/Support/ManagedStatic.cpp index 153884ba429..ad2fc977e6d 100644 --- a/unittests/Support/ManagedStatic.cpp +++ b/unittests/Support/ManagedStatic.cpp @@ -47,6 +47,7 @@ TEST(Initialize, MultipleThreads) { 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); @@ -54,6 +55,7 @@ TEST(Initialize, MultipleThreads) { pthread_join(t2, nullptr); free(p1); free(p2); + llvm_stop_multithreaded(); } #endif