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/ADT/Optional.h"
16 #include "llvm/Config/config.h"
17 #include "llvm/Support/Host.h"
18 
19 #include <cassert>
20 #include <errno.h>
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 bool llvm::llvm_is_multithreaded() {
32 #if LLVM_ENABLE_THREADS != 0
33   return true;
34 #else
35   return false;
36 #endif
37 }
38 
39 #if LLVM_ENABLE_THREADS == 0 ||                                                \
40     (!defined(_WIN32) && !defined(HAVE_PTHREAD_H))
41 uint64_t llvm::get_threadid() { return 0; }
42 
43 uint32_t llvm::get_max_thread_name_length() { return 0; }
44 
45 void llvm::set_thread_name(const Twine &Name) {}
46 
47 void llvm::get_thread_name(SmallVectorImpl<char> &Name) { Name.clear(); }
48 
49 llvm::BitVector llvm::get_thread_affinity_mask() { return {}; }
50 
51 unsigned llvm::ThreadPoolStrategy::compute_thread_count() const {
52   // When threads are disabled, ensure clients will loop at least once.
53   return 1;
54 }
55 
56 #else
57 
58 int computeHostNumHardwareThreads();
59 
60 unsigned llvm::ThreadPoolStrategy::compute_thread_count() const {
61   int MaxThreadCount = UseHyperThreads ? computeHostNumHardwareThreads()
62                                        : sys::getHostNumPhysicalCores();
63   if (MaxThreadCount <= 0)
64     MaxThreadCount = 1;
65   if (ThreadsRequested == 0)
66     return MaxThreadCount;
67   if (!Limit)
68     return ThreadsRequested;
69   return std::min((unsigned)MaxThreadCount, ThreadsRequested);
70 }
71 
72 // Include the platform-specific parts of this class.
73 #ifdef LLVM_ON_UNIX
74 #include "Unix/Threading.inc"
75 #endif
76 #ifdef _WIN32
77 #include "Windows/Threading.inc"
78 #endif
79 
80 // Must be included after Threading.inc to provide definition for llvm::thread
81 // because FreeBSD's condvar.h (included by user.h) misuses the "thread"
82 // keyword.
83 #include "llvm/Support/thread.h"
84 
85 #if defined(__APPLE__)
86   // Darwin's default stack size for threads except the main one is only 512KB,
87   // which is not enough for some/many normal LLVM compilations. This implements
88   // the same interface as std::thread but requests the same stack size as the
89   // main thread (8MB) before creation.
90 const llvm::Optional<unsigned> llvm::thread::DefaultStackSize = 8 * 1024 * 1024;
91 #else
92 const llvm::Optional<unsigned> llvm::thread::DefaultStackSize = None;
93 #endif
94 
95 
96 #endif
97 
98 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 None; // 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