如何获取 Windows 线程的返回值？
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How can you get the return value of a Windows thread?
提问by Sefu
I was just wondering if it is possible (and if so, how) to get the return value of a thread in C++ (Windows). I have several threads, and I use WaitForMultipleObjects(...)on them. This waits until a thread is done, and returns the index of said thread, and all is well. However, I want to be able to obtain the return value of the thread that finished using its handle.
我只是想知道是否有可能（如果有，如何）在 C++ (Windows) 中获取线程的返回值。我有几个线程，我使用WaitForMultipleObjects(...)它们。这会一直等到一个线程完成，并返回该线程的索引，一切都很好。但是，我希望能够获得使用完其句柄的线程的返回值。
For example:
例如：
DWORD WINAPI Thread1(void *parameter){
...
if(...) return 0;
else return -1;
}
DWORD WINAPI Thread2(void *parameter){
...
if(...) return 1;
else return 0;
}
int main(){
HANDLE t1 = CreateThread(0, 0, Thread1, NULL, 0, 0);
HANDLE t2 = CreateThread(0, 0, Thread2, NULL, 0, 0);
HANDLE *threads = new HANDLE[2];
threads[0] = t1;
threads[1] = t2;
int result = WaitForMultipleObjects(2, threads, false, INFINITE);
if(result == 0){
//get the threads value here:
int retVal = SomeFunction(t1); //What is SomeFunction?
}
...
}
I have tried to use GetExitCodeThread(thread)but I'm assuming this returns a system exit code, as it always gives me a very strange integer. Does anyone know a way, or a workaround?
我尝试使用，GetExitCodeThread(thread)但我假设这会返回一个系统退出代码，因为它总是给我一个非常奇怪的整数。有谁知道方法或解决方法？
回答by Don Reba
GetExitCodeThreadis the correct function. Here is the MSDN description of what it does:
GetExitCodeThread是正确的函数。这是它的作用的 MSDN 描述：
This function returns immediately. If the specified thread has not terminated and the function succeeds, the status returned is STILL_ACTIVE. If the thread has terminated and the function succeeds, the status returned is one of the following values:
- The exit value specified in the ExitThread or TerminateThread function.
- The return value from the thread function.
- The exit value of the thread's process.
该函数立即返回。如果指定线程未终止且函数成功，则返回状态为 STILL_ACTIVE。如果线程已终止并且函数成功，则返回的状态为以下值之一：
- 在 ExitThread 或 TerminateThread 函数中指定的退出值。
- 线程函数的返回值。
- 线程进程的退出值。
回答by Ajay
The problem with most programmer is that they don't pay attention to compiler warnings. At level 4 (/W4), the compiler produces following warning when returning -1from a function that is returning DWORD:
大多数程序员的问题是他们不注意编译器警告。在级别 4 (/W4)，编译器在-1从返回的函数返回时产生以下警告DWORD：
warning C4245: 'return' : conversion from 'int' to 'DWORD', signed/unsigned mismatch
warning C4245: 'return' : conversion from 'int' to 'DWORD', signed/unsigned mismatch
回答by shivakumar
You can use C++ 11's threads concepts using std::future.
See an example below.
您可以使用 C++ 11 的线程概念使用std::future.
请参阅下面的示例。
int ReturnFrmThread() {
return 100;
}
int main() {
std::future<int> GetRetVal= std::async(ReturnFrmThread); // Execution of ReturnFrmThread starts
int answer = GetAnAnswer.get(); // gets value as 100;
// Waits until ReturnFrmThread has finished
}
回答by AppDeveloper
you need to check for STILL_ACTIVE for the values one of these threads may still be active
您需要检查 STILL_ACTIVE 的值，这些线程之一可能仍处于活动状态
