From 6ad2444d5bfdeeb75b7cbeb672fc73fce342ec6b Mon Sep 17 00:00:00 2001 From: Zachary Turner Date: Thu, 19 Jun 2014 16:17:42 +0000 Subject: [PATCH] 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 --- llvm/docs/ProgrammersManual.rst | 5 ----- llvm/include/llvm/Support/Threading.h | 8 -------- llvm/lib/Support/ManagedStatic.cpp | 23 ++++++++++++++++++++--- llvm/lib/Support/Threading.cpp | 12 ------------ llvm/lib/Support/Timer.cpp | 4 ++-- 5 files changed, 22 insertions(+), 30 deletions(-) diff --git a/llvm/docs/ProgrammersManual.rst b/llvm/docs/ProgrammersManual.rst index 4973e5c66719..df3795a34d33 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 a7e8774558d5..d84d11867958 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 6a1c2a545a8d..9d7e99f97fb5 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 +#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. +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 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 Lock(GetManagedStaticMutex()); + while (StaticList) StaticList->destroy(); diff --git a/llvm/lib/Support/Threading.cpp b/llvm/lib/Support/Threading.cpp index 1acfa79b11d5..2358dde0e6c5 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 diff --git a/llvm/lib/Support/Timer.cpp b/llvm/lib/Support/Timer.cpp index 61465ae5e8be..210bda754e74 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 Lock(*TimerLock); tmp = DefaultTimerGroup; if (!tmp) { tmp = new TimerGroup("Miscellaneous Ungrouped Timers"); sys::MemoryFence(); DefaultTimerGroup = tmp; } - llvm_release_global_lock(); return tmp; }