LLVM  4.0.0
Threading.h
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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/Config/llvm-config.h" // for LLVM_ON_UNIX
19 #include "llvm/Support/Compiler.h"
20 #include <ciso646> // So we can check the C++ standard lib macros.
21 #include <functional>
22 
23 // std::call_once from libc++ is used on all Unix platforms. Other
24 // implementations like libstdc++ are known to have problems on NetBSD,
25 // OpenBSD and PowerPC.
26 #if defined(LLVM_ON_UNIX) && (defined(_LIBCPP_VERSION) || \
27  !(defined(__NetBSD__) || defined(__OpenBSD__) || defined(__ppc__)))
28 #define LLVM_THREADING_USE_STD_CALL_ONCE 1
29 #else
30 #define LLVM_THREADING_USE_STD_CALL_ONCE 0
31 #endif
32 
33 #if LLVM_THREADING_USE_STD_CALL_ONCE
34 #include <mutex>
35 #else
36 #include "llvm/Support/Atomic.h"
37 #endif
38 
39 namespace llvm {
40  /// Returns true if LLVM is compiled with support for multi-threading, and
41  /// false otherwise.
42  bool llvm_is_multithreaded();
43 
44  /// llvm_execute_on_thread - Execute the given \p UserFn on a separate
45  /// thread, passing it the provided \p UserData and waits for thread
46  /// completion.
47  ///
48  /// This function does not guarantee that the code will actually be executed
49  /// on a separate thread or honoring the requested stack size, but tries to do
50  /// so where system support is available.
51  ///
52  /// \param UserFn - The callback to execute.
53  /// \param UserData - An argument to pass to the callback function.
54  /// \param RequestedStackSize - If non-zero, a requested size (in bytes) for
55  /// the thread stack.
56  void llvm_execute_on_thread(void (*UserFn)(void*), void *UserData,
57  unsigned RequestedStackSize = 0);
58 
59 #if LLVM_THREADING_USE_STD_CALL_ONCE
60 
62 
63  /// This macro is the only way you should define your once flag for LLVM's
64  /// call_once.
65 #define LLVM_DEFINE_ONCE_FLAG(flag) static once_flag flag
66 
67 #else
68 
69  enum InitStatus { Uninitialized = 0, Wait = 1, Done = 2 };
70  typedef volatile sys::cas_flag once_flag;
71 
72  /// This macro is the only way you should define your once flag for LLVM's
73  /// call_once.
74 #define LLVM_DEFINE_ONCE_FLAG(flag) static once_flag flag = Uninitialized
75 
76 #endif
77 
78  /// \brief Execute the function specified as a parameter once.
79  ///
80  /// Typical usage:
81  /// \code
82  /// void foo() {...};
83  /// ...
84  /// LLVM_DEFINE_ONCE_FLAG(flag);
85  /// call_once(flag, foo);
86  /// \endcode
87  ///
88  /// \param flag Flag used for tracking whether or not this has run.
89  /// \param F Function to call once.
90  template <typename Function, typename... Args>
91  void call_once(once_flag &flag, Function &&F, Args &&... ArgList) {
92 #if LLVM_THREADING_USE_STD_CALL_ONCE
93  std::call_once(flag, std::forward<Function>(F),
94  std::forward<Args>(ArgList)...);
95 #else
96  // For other platforms we use a generic (if brittle) version based on our
97  // atomics.
98  sys::cas_flag old_val = sys::CompareAndSwap(&flag, Wait, Uninitialized);
99  if (old_val == Uninitialized) {
100  std::forward<Function>(F)(std::forward<Args>(ArgList)...);
103  TsanHappensBefore(&flag);
104  flag = Done;
106  } else {
107  // Wait until any thread doing the call has finished.
108  sys::cas_flag tmp = flag;
110  while (tmp != Done) {
111  tmp = flag;
113  }
114  }
115  TsanHappensAfter(&flag);
116 #endif
117  }
118 
119  /// Get the amount of currency to use for tasks requiring significant
120  /// memory or other resources. Currently based on physical cores, if
121  /// available for the host system, otherwise falls back to
122  /// thread::hardware_concurrency().
123  /// Returns 1 when LLVM is configured with LLVM_ENABLE_THREADS=OFF
125 }
126 
127 #endif
unsigned heavyweight_hardware_concurrency()
Get the amount of currency to use for tasks requiring significant memory or other resources...
Definition: Threading.cpp:121
void call_once(once_flag &flag, Function &&F, Args &&...ArgList)
Execute the function specified as a parameter once.
Definition: Threading.h:91
#define F(x, y, z)
Definition: MD5.cpp:51
cas_flag CompareAndSwap(volatile cas_flag *ptr, cas_flag new_value, cas_flag old_value)
#define TsanHappensAfter(cv)
Definition: Compiler.h:433
bool llvm_is_multithreaded()
Returns true if LLVM is compiled with support for multi-threading, and false otherwise.
Definition: Threading.cpp:25
#define TsanHappensBefore(cv)
Definition: Compiler.h:432
std::once_flag once_flag
Definition: Threading.h:61
void MemoryFence()
Definition: Atomic.cpp:29
void llvm_execute_on_thread(void(*UserFn)(void *), void *UserData, unsigned RequestedStackSize=0)
llvm_execute_on_thread - Execute the given UserFn on a separate thread, passing it the provided UserD...
Definition: Threading.cpp:46
#define TsanIgnoreWritesBegin()
Definition: Compiler.h:434
#define TsanIgnoreWritesEnd()
Definition: Compiler.h:435
uint32_t cas_flag
Definition: Atomic.h:30
ProcessInfo Wait(const ProcessInfo &PI, unsigned SecondsToWait, bool WaitUntilTerminates, std::string *ErrMsg=nullptr)
This function waits for the process specified by PI to finish.