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 <errno.h>
  20 #include <optional>
  21 #include <stdlib.h>
  22 #include <string.h>
  23
  24 using namespace llvm;
  25
  26 //===----------------------------------------------------------------------===//
  27 //=== WARNING: Implementation here must contain only TRULY operating system
  28 //===          independent code.
  29 //===----------------------------------------------------------------------===//
  30
  31 #if LLVM_ENABLE_THREADS == 0 ||                                                \
  32     (!defined(_WIN32) && !defined(HAVE_PTHREAD_H))
  33 uint64_t llvm::get_threadid() { return 0; }
  34
  35 uint32_t llvm::get_max_thread_name_length() { return 0; }
  36
  37 void llvm::set_thread_name(const Twine &Name) {}
  38
  39 void llvm::get_thread_name(SmallVectorImpl<char> &Name) { Name.clear(); }
  40
  41 llvm::BitVector llvm::get_thread_affinity_mask() { return {}; }
  42
  43 unsigned llvm::ThreadPoolStrategy::compute_thread_count() const {
  44   // When threads are disabled, ensure clients will loop at least once.
  45   return 1;
  46 }
  47
  48 // Unknown if threading turned off
  49 int llvm::get_physical_cores() { return -1; }
  50
  51 #else
  52
  53 static int computeHostNumHardwareThreads();
  54
  55 unsigned llvm::ThreadPoolStrategy::compute_thread_count() const {
  56   int MaxThreadCount =
  57       UseHyperThreads ? computeHostNumHardwareThreads() : get_physical_cores();
  58   if (MaxThreadCount <= 0)
  59     MaxThreadCount = 1;
  60   if (ThreadsRequested == 0)
  61     return MaxThreadCount;
  62   if (!Limit)
  63     return ThreadsRequested;
  64   return std::min((unsigned)MaxThreadCount, ThreadsRequested);
  65 }
  66
  67 // Include the platform-specific parts of this class.
  68 #ifdef LLVM_ON_UNIX
  69 #include "Unix/Threading.inc"
  70 #endif
  71 #ifdef _WIN32
  72 #include "Windows/Threading.inc"
  73 #endif
  74
  75 // Must be included after Threading.inc to provide definition for llvm::thread
  76 // because FreeBSD's condvar.h (included by user.h) misuses the "thread"
  77 // keyword.
  78 #include "llvm/Support/thread.h"
  79
  80 #if defined(__APPLE__)
  81   // Darwin's default stack size for threads except the main one is only 512KB,
  82   // which is not enough for some/many normal LLVM compilations. This implements
  83   // the same interface as std::thread but requests the same stack size as the
  84   // main thread (8MB) before creation.
  85 const std::optional<unsigned> llvm::thread::DefaultStackSize = 8 * 1024 * 1024;
  86 #elif defined(_AIX)
  87   // On AIX, the default pthread stack size limit is ~192k for 64-bit programs.
  88   // This limit is easily reached when doing link-time thinLTO. AIX library
  89   // developers have used 4MB, so we'll do the same.
  90 const std::optional<unsigned> llvm::thread::DefaultStackSize = 4 * 1024 * 1024;
  91 #else
  92 const std::optional<unsigned> llvm::thread::DefaultStackSize;
  93 #endif
  94
  95
  96 #endif
  97
  98 std::optional<ThreadPoolStrategy>
  99 llvm::get_threadpool_strategy(StringRef Num, ThreadPoolStrategy Default) {
 100   if (Num == "all")
 101     return llvm::hardware_concurrency();
 102   if (Num.empty())
 103     return Default;
 104   unsigned V;
 105   if (Num.getAsInteger(10, V))
 106     return std::nullopt; // malformed 'Num' value
 107   if (V == 0)
 108     return Default;
 109
 110   // Do not take the Default into account. This effectively disables
 111   // heavyweight_hardware_concurrency() if the user asks for any number of
 112   // threads on the cmd-line.
 113   ThreadPoolStrategy S = llvm::hardware_concurrency();
 114   S.ThreadsRequested = V;
 115   return S;
 116 }