From cdde33ebaad211e1ce0fc22b53bbccff8bb3c1a4 Mon Sep 17 00:00:00 2001 From: NAKAMURA Takumi Date: Tue, 24 Jun 2014 13:36:31 +0000 Subject: Revert r211287, "Remove support for LLVM runtime multi-threading." libclang still requires it on cygming, lack of incomplete . git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211592 91177308-0d34-0410-b5e6-96231b3b80d8 --- docs/ProgrammersManual.rst | 45 ++++++++++++++++++++++++++++++++---- include/llvm-c/Core.h | 13 +++++++---- include/llvm/Support/ManagedStatic.h | 3 +++ include/llvm/Support/Threading.h | 21 +++++++++++++---- lib/IR/Core.cpp | 3 ++- lib/Support/Threading.cpp | 29 ++++++++++++++++++++--- unittests/Support/ManagedStatic.cpp | 2 ++ 7 files changed, 99 insertions(+), 17 deletions(-) diff --git a/docs/ProgrammersManual.rst b/docs/ProgrammersManual.rst index a7b28b36ca..df3795a34d 100644 --- a/docs/ProgrammersManual.rst +++ b/docs/ProgrammersManual.rst @@ -2170,13 +2170,46 @@ 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: @@ -2184,11 +2217,15 @@ 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. + .. _llvmcontext: Achieving Isolation with ``LLVMContext`` diff --git a/include/llvm-c/Core.h b/include/llvm-c/Core.h index 8693a3020a..0e78ed71fa 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 d8fbfeb8e2..1bb8cea092 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/Threading.h b/include/llvm/Support/Threading.h index 7e8758407c..d84d118679 100644 --- a/include/llvm/Support/Threading.h +++ b/include/llvm/Support/Threading.h @@ -7,8 +7,7 @@ // //===----------------------------------------------------------------------===// // -// This file declares helper functions for running LLVM in a multi-threaded -// environment. +// TThis file defines llvm_start_multithreaded() and friends. // //===----------------------------------------------------------------------===// @@ -16,8 +15,22 @@ #define LLVM_SUPPORT_THREADING_H namespace llvm { - /// Returns true if LLVM is compiled with support for multi-threading, 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(); /// llvm_execute_on_thread - Execute the given \p UserFn on a separate diff --git a/lib/IR/Core.cpp b/lib/IR/Core.cpp index 0cb781c2c6..2c49d5b949 100644 --- a/lib/IR/Core.cpp +++ b/lib/IR/Core.cpp @@ -2708,10 +2708,11 @@ 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/Threading.cpp b/lib/Support/Threading.cpp index ca7f3f64aa..2358dde0e6 100644 --- a/lib/Support/Threading.cpp +++ b/lib/Support/Threading.cpp @@ -7,8 +7,7 @@ // //===----------------------------------------------------------------------===// // -// This file defines helper functions for running LLVM in a multi-threaded -// environment. +// This file implements llvm_start_multithreaded() and friends. // //===----------------------------------------------------------------------===// @@ -20,14 +19,38 @@ using namespace llvm; -bool llvm::llvm_is_multithreaded() { +static bool multithreaded_mode = false; + +bool llvm::llvm_start_multithreaded() { #if LLVM_ENABLE_THREADS != 0 + assert(!multithreaded_mode && "Already multithreaded!"); + multithreaded_mode = 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; +#endif +} + +bool llvm::llvm_is_multithreaded() { + return multithreaded_mode; +} + #if LLVM_ENABLE_THREADS != 0 && defined(HAVE_PTHREAD_H) #include diff --git a/unittests/Support/ManagedStatic.cpp b/unittests/Support/ManagedStatic.cpp index 153884ba42..ad2fc977e6 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 -- cgit v1.2.3