libcxx/test/std/thread/thread.jthread/join.pass.cpp

   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 // UNSUPPORTED: no-threads
  10 // UNSUPPORTED: c++03, c++11, c++14, c++17
  11 // XFAIL: availability-synchronization_library-missing
  12
  13 // void join();
  14
  15 #include <atomic>
  16 #include <cassert>
  17 #include <chrono>
  18 #include <concepts>
  19 #include <functional>
  20 #include <system_error>
  21 #include <thread>
  22 #include <type_traits>
  23 #include <vector>
  24
  25 #include "make_test_thread.h"
  26 #include "test_macros.h"
  27
  28 int main(int, char**) {
  29   // Effects: Blocks until the thread represented by *this has completed.
  30   {
  31     std::atomic_int calledTimes = 0;
  32     std::vector<std::jthread> jts;
  33     constexpr auto numberOfThreads = 10u;
  34     jts.reserve(numberOfThreads);
  35     for (auto i = 0u; i < numberOfThreads; ++i) {
  36       jts.emplace_back(support::make_test_jthread([&] {
  37         std::this_thread::sleep_for(std::chrono::milliseconds(2));
  38         calledTimes.fetch_add(1, std::memory_order_relaxed);
  39       }));
  40     }
  41
  42     for (auto i = 0u; i < numberOfThreads; ++i) {
  43       jts[i].join();
  44     }
  45
  46     // If join did block, calledTimes must equal to numberOfThreads
  47     // If join did not block, there is a chance that the check below happened
  48     // before test threads incrementing the counter, thus calledTimed would
  49     // be less than numberOfThreads.
  50     // This is not going to catch issues 100%. Creating more threads to increase
  51     // the probability of catching the issue
  52     assert(calledTimes.load(std::memory_order_relaxed) == numberOfThreads);
  53   }
  54
  55   // Synchronization: The completion of the thread represented by *this synchronizes with
  56   // ([intro.multithread]) the corresponding successful join() return.
  57   {
  58     bool flag       = false;
  59     std::jthread jt = support::make_test_jthread([&] { flag = true; });
  60     jt.join();
  61     assert(flag); // non atomic write is visible to the current thread
  62   }
  63
  64   // Postconditions: The thread represented by *this has completed. get_id() == id().
  65   {
  66     std::jthread jt = support::make_test_jthread([] {});
  67     assert(jt.get_id() != std::jthread::id());
  68     jt.join();
  69     assert(jt.get_id() == std::jthread::id());
  70   }
  71
  72 #if !defined(TEST_HAS_NO_EXCEPTIONS)
  73   // Throws: system_error when an exception is required ([thread.req.exception]).
  74   // invalid_argument - if the thread is not joinable.
  75   {
  76     std::jthread jt;
  77     try {
  78       jt.join();
  79       assert(false);
  80     } catch (const std::system_error& err) {
  81       assert(err.code() == std::errc::invalid_argument);
  82     }
  83   }
  84
  85 #endif
  86
  87   return 0;
  88 }