std::future::wait_for
STD：：未来：等待[医]为
| template< class Rep, class Period > std::future_status wait_for( const std::chrono::duration | | (since C++11) |
|---|
等待结果可用。块，直到指定timeout_duration已过或结果可用，以第一位为准。返回值标识结果的状态。
用一个稳定的时钟来测量持续时间。此函数的阻塞时间可能超过timeout_duration由于调度或资源争用延迟。
如果valid()== false在调用此函数之前。
参数
| timeout_duration | - | maximum duration to block for |
|---|
返回值
| Constant | Explanation |
|---|---|
| future_status::deferred | The function to calculate the result has not been started yet |
| future_status::ready | The result is ready |
| future_status::timeout | The timeout has expired |
例外
任何由时钟、时间引发的异常[医]在执行%28时钟、时间点和标准库提供的持续时间期间，不要抛出%29。
注记
鼓励实现在下列情况下检测情况：valid == false在呼叫前抛出一个future_error错误条件为future_errc::no_state...
例
二次
#include <iostream>
#include <future>
#include <thread>
#include <chrono>
int main()
{
std::future<int> future = std::async(std::launch::async, [](){
std::this_thread::sleep_for(std::chrono::seconds(3)
return 8;
}
std::cout << "waiting...\n";
std::future_status status;
do {
status = future.wait_for(std::chrono::seconds(1)
if (status == std::future_status::deferred) {
std::cout << "deferred\n";
} else if (status == std::future_status::timeout) {
std::cout << "timeout\n";
} else if (status == std::future_status::ready) {
std::cout << "ready!\n";
}
} while (status != std::future_status::ready
std::cout << "result is " << future.get() << '\n';
}
二次
可能的产出：
二次
waiting...
timeout
timeout
ready!
result is 8
二次
另见
| wait | waits for the result to become available (public member function) |
|---|---|
| wait_until | waits for the result, returns if it is not available until specified time point has been reached (public member function) |
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