1//===----------------------------------------------------------------------===//
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#include <algorithm>
10#include <random>
11
12#ifndef _LIBCPP_HAS_NO_THREADS
13# include <mutex>
14# if defined(__ELF__) && defined(_LIBCPP_LINK_PTHREAD_LIB)
15# pragma comment(lib, "pthread")
16# endif
17#endif
18
19_LIBCPP_BEGIN_NAMESPACE_STD
20
21#ifndef _LIBCPP_HAS_NO_THREADS
22static constinit __libcpp_mutex_t __rs_mut = _LIBCPP_MUTEX_INITIALIZER;
23#endif
24unsigned __rs_default::__c_ = 0;
25
26__rs_default::__rs_default() {
27#ifndef _LIBCPP_HAS_NO_THREADS
28 __libcpp_mutex_lock(&__rs_mut);
29#endif
30 __c_ = 1;
31}
32
33__rs_default::__rs_default(const __rs_default&) { ++__c_; }
34
35__rs_default::~__rs_default() {
36#ifndef _LIBCPP_HAS_NO_THREADS
37 if (--__c_ == 0)
38 __libcpp_mutex_unlock(&__rs_mut);
39#else
40 --__c_;
41#endif
42}
43
44__rs_default::result_type __rs_default::operator()() {
45 static mt19937 __rs_g;
46 return __rs_g();
47}
48
49__rs_default __rs_get() { return __rs_default(); }
50
51_LIBCPP_END_NAMESPACE_STD
52

source code of libcxx/src/random_shuffle.cpp