From a4d0ff9cd1fb3fe4c3a58d0747dc523f7d9e9e3f Mon Sep 17 00:00:00 2001 From: Zachary Turner Date: Thu, 19 Jun 2014 18:18:23 +0000 Subject: [PATCH] Remove support for LLVM runtime multi-threading. After a number of previous small iterations, the functions llvm_start_multithreaded() and llvm_stop_multithreaded() have been reduced essentially to no-ops. This change removes them entirely. Reviewed by: rnk, dblaikie Differential Revision: http://reviews.llvm.org/D4216 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211287 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 | 23 ++++---------- lib/IR/Core.cpp | 3 +- lib/Support/Threading.cpp | 29 ++---------------- unittests/Support/ManagedStatic.cpp | 2 -- 7 files changed, 19 insertions(+), 99 deletions(-) diff --git a/docs/ProgrammersManual.rst b/docs/ProgrammersManual.rst index df3795a34d3..a7b28b36ca1 100644 --- a/docs/ProgrammersManual.rst +++ b/docs/ProgrammersManual.rst @@ -2170,46 +2170,13 @@ 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. 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: @@ -2217,15 +2184,11 @@ 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. - .. _llvmcontext: Achieving Isolation with ``LLVMContext`` diff --git a/include/llvm-c/Core.h b/include/llvm-c/Core.h index 0e78ed71fa9..8693a3020ab 100644 --- a/include/llvm-c/Core.h +++ b/include/llvm-c/Core.h @@ -2848,16 +2848,13 @@ void LLVMDisposePassManager(LLVMPassManagerRef PM); * @{ */ -/** 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. diff --git a/include/llvm/Support/ManagedStatic.h b/include/llvm/Support/ManagedStatic.h index 1bb8cea092f..d8fbfeb8e20 100644 --- a/include/llvm/Support/ManagedStatic.h +++ b/include/llvm/Support/ManagedStatic.h @@ -103,9 +103,6 @@ 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 d84d1186795..981971bd1e8 100644 --- a/include/llvm/Support/Threading.h +++ b/include/llvm/Support/Threading.h @@ -7,30 +7,19 @@ // //===----------------------------------------------------------------------===// // -// TThis file defines llvm_start_multithreaded() and friends. +// This file declares helper functions for running LLVM in a multi-threaded +// environment. // //===----------------------------------------------------------------------===// #ifndef LLVM_SUPPORT_THREADING_H #define LLVM_SUPPORT_THREADING_H +#include "llvm/Support/Mutex.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(); - - /// llvm_is_multithreaded - Check whether LLVM is executing in thread-safe - /// mode or not. + /// Returns true if LLVM is compiled with support for multi-threading, and + /// false otherwise. 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 197b6cb9054..68b9baa2baa 100644 --- a/lib/IR/Core.cpp +++ b/lib/IR/Core.cpp @@ -2702,11 +2702,10 @@ void LLVMDisposePassManager(LLVMPassManagerRef PM) { /*===-- Threading ------------------------------------------------------===*/ LLVMBool LLVMStartMultithreaded() { - return llvm_start_multithreaded(); + return LLVMIsMultithreaded(); } void LLVMStopMultithreaded() { - llvm_stop_multithreaded(); } LLVMBool LLVMIsMultithreaded() { diff --git a/lib/Support/Threading.cpp b/lib/Support/Threading.cpp index 2358dde0e6c..ca7f3f64aa3 100644 --- a/lib/Support/Threading.cpp +++ b/lib/Support/Threading.cpp @@ -7,7 +7,8 @@ // //===----------------------------------------------------------------------===// // -// This file implements llvm_start_multithreaded() and friends. +// This file defines helper functions for running LLVM in a multi-threaded +// environment. // //===----------------------------------------------------------------------===// @@ -19,38 +20,14 @@ using namespace llvm; -static bool multithreaded_mode = false; - -bool llvm::llvm_start_multithreaded() { +bool llvm::llvm_is_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 ad2fc977e6d..153884ba429 100644 --- a/unittests/Support/ManagedStatic.cpp +++ b/unittests/Support/ManagedStatic.cpp @@ -47,7 +47,6 @@ 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); @@ -55,7 +54,6 @@ TEST(Initialize, MultipleThreads) { pthread_join(t2, nullptr); free(p1); free(p2); - llvm_stop_multithreaded(); } #endif