1 //===-- llvm/Support/Threading.h - Control multithreading mode --*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file declares helper functions for running LLVM in a multi-threaded
13 //===----------------------------------------------------------------------===//
15 #ifndef LLVM_SUPPORT_THREADING_H
16 #define LLVM_SUPPORT_THREADING_H
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.
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
36 #define LLVM_THREADING_USE_STD_CALL_ONCE 0
39 #if LLVM_THREADING_USE_STD_CALL_ONCE
42 #include "llvm/Support/Atomic.h"
48 /// Returns true if LLVM is compiled with support for multi-threading, and
50 bool llvm_is_multithreaded();
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
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.
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
64 void llvm_execute_on_thread(void (*UserFn)(void *), void *UserData,
65 unsigned RequestedStackSize = 0);
67 #if LLVM_THREADING_USE_STD_CALL_ONCE
69 typedef std::once_flag once_flag;
73 enum InitStatus { Uninitialized = 0, Wait = 1, Done = 2 };
75 /// \brief The llvm::once_flag structure
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.
81 volatile sys::cas_flag status = Uninitialized;
86 /// \brief Execute the function specified as a parameter once.
92 /// static once_flag flag;
93 /// call_once(flag, foo);
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)...);
104 // For other platforms we use a generic (if brittle) version based on our
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)...);
110 TsanIgnoreWritesBegin();
111 TsanHappensBefore(&flag.status);
113 TsanIgnoreWritesEnd();
115 // Wait until any thread doing the call has finished.
116 sys::cas_flag tmp = flag.status;
118 while (tmp != Done) {
123 TsanHappensAfter(&flag.status);
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();
134 /// Get the number of threads that the current program can execute
135 /// concurrently. On some systems std::thread::hardware_concurrency() returns
136 /// the total number of cores, without taking affinity into consideration.
137 /// Returns 1 when LLVM is configured with LLVM_ENABLE_THREADS=OFF.
138 /// Fallback to std::thread::hardware_concurrency() if sched_getaffinity is
140 unsigned hardware_concurrency();
142 /// \brief Return the current thread id, as used in various OS system calls.
143 /// Note that not all platforms guarantee that the value returned will be
144 /// unique across the entire system, so portable code should not assume
146 uint64_t get_threadid();
148 /// \brief Get the maximum length of a thread name on this platform.
149 /// A value of 0 means there is no limit.
150 uint32_t get_max_thread_name_length();
152 /// \brief Set the name of the current thread. Setting a thread's name can
153 /// be helpful for enabling useful diagnostics under a debugger or when
154 /// logging. The level of support for setting a thread's name varies
155 /// wildly across operating systems, and we only make a best effort to
156 /// perform the operation on supported platforms. No indication of success
157 /// or failure is returned.
158 void set_thread_name(const Twine &Name);
160 /// \brief Get the name of the current thread. The level of support for
161 /// getting a thread's name varies wildly across operating systems, and it
162 /// is not even guaranteed that if you can successfully set a thread's name
163 /// that you can later get it back. This function is intended for diagnostic
164 /// purposes, and as with setting a thread's name no indication of whether
165 /// the operation succeeded or failed is returned.
166 void get_thread_name(SmallVectorImpl<char> &Name);