1 //===-- llvm/Support/Threading.h - Control multithreading mode --*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file declares helper functions for running LLVM in a multi-threaded 11 // environment. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #ifndef LLVM_SUPPORT_THREADING_H 16 #define LLVM_SUPPORT_THREADING_H 17 18 #include "llvm/ADT/SmallVector.h" 19 #include "llvm/Config/llvm-config.h" // for LLVM_ON_UNIX 20 #include "llvm/Support/Compiler.h" 21 #include <ciso646> // So we can check the C++ standard lib macros. 22 #include <functional> 23 24 #if defined(_MSC_VER) 25 // MSVC's call_once implementation worked since VS 2015, which is the minimum 26 // supported version as of this writing. 27 #define LLVM_THREADING_USE_STD_CALL_ONCE 1 28 #elif defined(LLVM_ON_UNIX) && \ 29 (defined(_LIBCPP_VERSION) || \ 30 !(defined(__NetBSD__) || defined(__OpenBSD__) || defined(__ppc__))) 31 // std::call_once from libc++ is used on all Unix platforms. Other 32 // implementations like libstdc++ are known to have problems on NetBSD, 33 // OpenBSD and PowerPC. 34 #define LLVM_THREADING_USE_STD_CALL_ONCE 1 35 #else 36 #define LLVM_THREADING_USE_STD_CALL_ONCE 0 37 #endif 38 39 #if LLVM_THREADING_USE_STD_CALL_ONCE 40 #include <mutex> 41 #else 42 #include "llvm/Support/Atomic.h" 43 #endif 44 45 namespace llvm { 46 class Twine; 47 48 /// Returns true if LLVM is compiled with support for multi-threading, and 49 /// false otherwise. 50 bool llvm_is_multithreaded(); 51 52 /// llvm_execute_on_thread - Execute the given \p UserFn on a separate 53 /// thread, passing it the provided \p UserData and waits for thread 54 /// completion. 55 /// 56 /// This function does not guarantee that the code will actually be executed 57 /// on a separate thread or honoring the requested stack size, but tries to do 58 /// so where system support is available. 59 /// 60 /// \param UserFn - The callback to execute. 61 /// \param UserData - An argument to pass to the callback function. 62 /// \param RequestedStackSize - If non-zero, a requested size (in bytes) for 63 /// the thread stack. 64 void llvm_execute_on_thread(void (*UserFn)(void *), void *UserData, 65 unsigned RequestedStackSize = 0); 66 67 #if LLVM_THREADING_USE_STD_CALL_ONCE 68 69 typedef std::once_flag once_flag; 70 71 #else 72 73 enum InitStatus { Uninitialized = 0, Wait = 1, Done = 2 }; 74 75 /// \brief The llvm::once_flag structure 76 /// 77 /// This type is modeled after std::once_flag to use with llvm::call_once. 78 /// This structure must be used as an opaque object. It is a struct to force 79 /// autoinitialization and behave like std::once_flag. 80 struct once_flag { 81 volatile sys::cas_flag status = Uninitialized; 82 }; 83 84 #endif 85 86 /// \brief Execute the function specified as a parameter once. 87 /// 88 /// Typical usage: 89 /// \code 90 /// void foo() {...}; 91 /// ... 92 /// static once_flag flag; 93 /// call_once(flag, foo); 94 /// \endcode 95 /// 96 /// \param flag Flag used for tracking whether or not this has run. 97 /// \param F Function to call once. 98 template <typename Function, typename... Args> 99 void call_once(once_flag &flag, Function &&F, Args &&... ArgList) { 100 #if LLVM_THREADING_USE_STD_CALL_ONCE 101 std::call_once(flag, std::forward<Function>(F), 102 std::forward<Args>(ArgList)...); 103 #else 104 // For other platforms we use a generic (if brittle) version based on our 105 // atomics. 106 sys::cas_flag old_val = sys::CompareAndSwap(&flag.status, Wait, Uninitialized); 107 if (old_val == Uninitialized) { 108 std::forward<Function>(F)(std::forward<Args>(ArgList)...); 109 sys::MemoryFence(); 110 TsanIgnoreWritesBegin(); 111 TsanHappensBefore(&flag.status); 112 flag.status = Done; 113 TsanIgnoreWritesEnd(); 114 } else { 115 // Wait until any thread doing the call has finished. 116 sys::cas_flag tmp = flag.status; 117 sys::MemoryFence(); 118 while (tmp != Done) { 119 tmp = flag.status; 120 sys::MemoryFence(); 121 } 122 } 123 TsanHappensAfter(&flag.status); 124 #endif 125 } 126 127 /// Get the amount of currency to use for tasks requiring significant 128 /// memory or other resources. Currently based on physical cores, if 129 /// available for the host system, otherwise falls back to 130 /// thread::hardware_concurrency(). 131 /// Returns 1 when LLVM is configured with LLVM_ENABLE_THREADS=OFF 132 unsigned heavyweight_hardware_concurrency(); 133 134 /// \brief Return the current thread id, as used in various OS system calls. 135 /// Note that not all platforms guarantee that the value returned will be 136 /// unique across the entire system, so portable code should not assume 137 /// this. 138 uint64_t get_threadid(); 139 140 /// \brief Get the maximum length of a thread name on this platform. 141 /// A value of 0 means there is no limit. 142 uint32_t get_max_thread_name_length(); 143 144 /// \brief Set the name of the current thread. Setting a thread's name can 145 /// be helpful for enabling useful diagnostics under a debugger or when 146 /// logging. The level of support for setting a thread's name varies 147 /// wildly across operating systems, and we only make a best effort to 148 /// perform the operation on supported platforms. No indication of success 149 /// or failure is returned. 150 void set_thread_name(const Twine &Name); 151 152 /// \brief Get the name of the current thread. The level of support for 153 /// getting a thread's name varies wildly across operating systems, and it 154 /// is not even guaranteed that if you can successfully set a thread's name 155 /// that you can later get it back. This function is intended for diagnostic 156 /// purposes, and as with setting a thread's name no indication of whether 157 /// the operation succeeded or failed is returned. 158 void get_thread_name(SmallVectorImpl<char> &Name); 159 } 160 161 #endif 162
