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C++ 11 thread 執行緒管理

std::thread 在 <thread> 標頭檔案中宣告,因此使用 std::thread 時需要包含 <thread> 標頭檔案。

std::thread 構造

default (1)
thread() noexcept;
initialization (2)
template <class Fn, class... Args>
explicit thread (Fn&& fn, Args&&... args);
copy [deleted] (3)
thread (const thread&) = delete;
move (4)
thread (thread&& x) noexcept;
  • (1). 預設建構函式,建立一個空的 thread 執行物件。
  • (2). 初始化建構函式,建立一個 thread物件,該 thread物件可被 joinable,新產生的執行緒會呼叫 fn 函式,該函式的引數由 args 給出。
  • (3). 拷貝建構函式(被禁用),意味著 thread 不可被拷貝構造。
  • (4). move 建構函式,move 建構函式,呼叫成功之後 x 不代表任何 thread 執行物件。
  • 注意:可被 joinable 的 thread 物件必須在他們銷燬之前被主執行緒 join 或者將其設定為 detached.

std::thread 各種建構函式例子如下(參考):

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#include <iostream>
#include <utility>
#include <thread>
#include <chrono>
#include <functional>
#include <atomic>
 
void f1(int n)
{
    for (int i = 0; i < 5; ++i) {
        std::cout << "Thread " << n << " executing\n
"; std::this_thread::sleep_for(std::chrono::milliseconds(10)); } } void f2(int& n) { for (int i = 0; i < 5; ++i) { std::cout << "Thread 2 executing\n"; ++n; std::this_thread::sleep_for(std::chrono::milliseconds(10)); } } int main() { int n = 0; std::thread t1; // t1 is not a thread std::thread t2(f1, n + 1); // pass by value std::thread t3(f2, std::ref(n)); // pass by reference std::thread t4(std::move(t3)); // t4 is now running f2(). t3 is no longer a thread t2.join(); t4.join(); std::cout << "Final value of n is " << n << '\n'; }
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move 賦值操作

move (1)
thread& operator= (thread&& rhs) noexcept;
copy [deleted] (2)
thread& operator= (const thread&) = delete;
  • (1). move 賦值操作,如果當前物件不可 joinable,需要傳遞一個右值引用(rhs)給 move 賦值操作;如果當前物件可被 joinable,則 terminate() 報錯。
  • (2). 拷貝賦值操作被禁用,thread 物件不可被拷貝。

請看下面的例子:

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#include <stdio.h>
#include <stdlib.h>

#include <chrono>    // std::chrono::seconds
#include <iostream>  // std::cout
#include <thread>    // std::thread, std::this_thread::sleep_for

void thread_task(int n) {
    std::this_thread::sleep_for(std::chrono::seconds(n));
    std::cout << "hello thread "
        << std::this_thread::get_id()
        << " paused " << n << " seconds" << std::endl;
}

/*
 * ===  FUNCTION  =========================================================
 *         Name:  main
 *  Description:  program entry routine.
 * ========================================================================
 */
int main(int argc, const char *argv[])
{
    std::thread threads[5];
    std::cout << "Spawning 5 threads...\n";
    for (int i = 0; i < 5; i++) {
        threads[i] = std::thread(thread_task, i + 1);
    }
    std::cout << "Done spawning threads! Now wait for them to join\n";
    for (auto& t: threads) {
        t.join();
    }
    std::cout << "All threads joined.\n";

    return EXIT_SUCCESS;
}  /* ----------  end of function main  ---------- */
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其他成員函式