llvm/lib/Support/Threading.cpp

   1 //===-- llvm/Support/Threading.cpp- Control multithreading mode --*- C++ -*-==//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file defines helper functions for running LLVM in a multi-threaded
  10 // environment.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/Support/Threading.h"
  15 #include "llvm/Config/config.h"
  16 #include "llvm/Config/llvm-config.h"
  17
  18 #include <cassert>
  19 #include <optional>
  20 #include <stdlib.h>
  21
  22 using namespace llvm;
  23
  24 //===----------------------------------------------------------------------===//
  25 //=== WARNING: Implementation here must contain only TRULY operating system
  26 //===          independent code.
  27 //===----------------------------------------------------------------------===//
  28
  29 #if LLVM_ENABLE_THREADS == 0 ||                                                \
  30     (!defined(_WIN32) && !defined(HAVE_PTHREAD_H))
  31 uint64_t llvm::get_threadid() { return 0; }
  32
  33 uint32_t llvm::get_max_thread_name_length() { return 0; }
  34
  35 void llvm::set_thread_name(const Twine &Name) {}
  36
  37 void llvm::get_thread_name(SmallVectorImpl<char> &Name) { Name.clear(); }
  38
  39 llvm::BitVector llvm::get_thread_affinity_mask() { return {}; }
  40
  41 unsigned llvm::ThreadPoolStrategy::compute_thread_count() const {
  42   // When threads are disabled, ensure clients will loop at least once.
  43   return 1;
  44 }
  45
  46 // Unknown if threading turned off
  47 int llvm::get_physical_cores() { return -1; }
  48
  49 #else
  50
  51 static int computeHostNumHardwareThreads();
  52
  53 unsigned llvm::ThreadPoolStrategy::compute_thread_count() const {
  54   int MaxThreadCount =
  55       UseHyperThreads ? computeHostNumHardwareThreads() : get_physical_cores();
  56   if (MaxThreadCount <= 0)
  57     MaxThreadCount = 1;
  58   if (ThreadsRequested == 0)
  59     return MaxThreadCount;
  60   if (!Limit)
  61     return ThreadsRequested;
  62   return std::min((unsigned)MaxThreadCount, ThreadsRequested);
  63 }
  64
  65 // Include the platform-specific parts of this class.
  66 #ifdef LLVM_ON_UNIX
  67 #include "Unix/Threading.inc"
  68 #endif
  69 #ifdef _WIN32
  70 #include "Windows/Threading.inc"
  71 #endif
  72
  73 // Must be included after Threading.inc to provide definition for llvm::thread
  74 // because FreeBSD's condvar.h (included by user.h) misuses the "thread"
  75 // keyword.
  76 #include "llvm/Support/thread.h"
  77
  78 #if defined(__APPLE__)
  79   // Darwin's default stack size for threads except the main one is only 512KB,
  80   // which is not enough for some/many normal LLVM compilations. This implements
  81   // the same interface as std::thread but requests the same stack size as the
  82   // main thread (8MB) before creation.
  83 const std::optional<unsigned> llvm::thread::DefaultStackSize = 8 * 1024 * 1024;
  84 #elif defined(_AIX)
  85   // On AIX, the default pthread stack size limit is ~192k for 64-bit programs.
  86   // This limit is easily reached when doing link-time thinLTO. AIX library
  87   // developers have used 4MB, so we'll do the same.
  88 const std::optional<unsigned> llvm::thread::DefaultStackSize = 4 * 1024 * 1024;
  89 #else
  90 const std::optional<unsigned> llvm::thread::DefaultStackSize;
  91 #endif
  92
  93
  94 #endif
  95
  96 std::optional<ThreadPoolStrategy>
  97 llvm::get_threadpool_strategy(StringRef Num, ThreadPoolStrategy Default) {
  98   if (Num == "all")
  99     return llvm::hardware_concurrency();
 100   if (Num.empty())
 101     return Default;
 102   unsigned V;
 103   if (Num.getAsInteger(10, V))
 104     return std::nullopt; // malformed 'Num' value
 105   if (V == 0)
 106     return Default;
 107
 108   // Do not take the Default into account. This effectively disables
 109   // heavyweight_hardware_concurrency() if the user asks for any number of
 110   // threads on the cmd-line.
 111   ThreadPoolStrategy S = llvm::hardware_concurrency();
 112   S.ThreadsRequested = V;
 113   return S;
 114 }