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
24using 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))
33uint64_t llvm::get_threadid() { return 0; }
34
35uint32_t llvm::get_max_thread_name_length() { return 0; }
36
37void llvm::set_thread_name(const Twine &Name) {}
38
39void llvm::get_thread_name(SmallVectorImpl<char> &Name) { Name.clear(); }
40
41llvm::BitVector llvm::get_thread_affinity_mask() { return {}; }
42
43unsigned 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
49int llvm::get_physical_cores() { return -1; }
50
51#else
52
53static int computeHostNumHardwareThreads();
54
55unsigned 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(a: (unsigned)MaxThreadCount, b: 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.
85const 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.
90const std::optional<unsigned> llvm::thread::DefaultStackSize = 4 * 1024 * 1024;
91#else
92const std::optional<unsigned> llvm::thread::DefaultStackSize;
93#endif
94
95
96#endif
97
98std::optional<ThreadPoolStrategy>
99llvm::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(Radix: 10, Result&: 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}
117

source code of llvm/lib/Support/Threading.cpp