Linux：fork＆execv，等待subprocess挂起

我写了一个辅助函数来启动一个使用fork（）和execv（）这个答案的过程 。 它用于启动例如mysqldump来进行数据库备份。 代码在不同程序的不同位置工作得很好。

现在我击中了一个失败的星座：这是一个呼叫systemctl来停止一个单位。 运行systemctl工作，单位停止。 但是在中间进程中，等待（）进程的时候，wait（）挂起，直到超时过程结束。 如果我检查，如果工作进程完成kill（），我可以告诉它。

重要提示：除了wait（）不表示工作进程结束之外，程序不会出现错误或故障。 我的代码中有什么（见下文）是不正确的，可能会触发这种行为？ 我已经读过Threads和fork（）：在混合它们之前三思，但是我找不到与我的问题有关的任何东西。

奇怪的是：程序中使用了深度，深度和深度的JSON-RPC。 如果我停用使用JSON-RPC的代码，一切正常！？

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环境：使用该function的程序是一个multithreading应用程序。 所有线程的信号都被阻塞。 主线程通过sigtimedwait（）处理信号。

代码（通过std :: cout输出日志logging的生产代码）和样本主函数：

#include <iostream> #include <unistd.h> #include <sys/wait.h> namespace { bool checkStatus(const int status) { return( WIFEXITED(status) && ( WEXITSTATUS(status) == 0 ) ); } } bool startProcess(const char* const path, const char* const argv[], const unsigned int timeoutInSeconds, pid_t& processId, const int* const fileDescriptor) { auto result = true; const pid_t intermediatePid = fork(); if(intermediatePid == 0) { // intermediate process std::cout << "Intermediate process: Started (" << getpid() << ")." << std::endl; const pid_t workerPid = fork(); if(workerPid == 0) { // worker process if(fileDescriptor) { std::cout << "Worker process: Redirecting file descriptor to stdin." << std::endl; const auto dupResult = dup2(*fileDescriptor, STDIN_FILENO); if(-1 == dupResult) { std::cout << "Worker process: Duplication of file descriptor failed." << std::endl; _exit(EXIT_FAILURE); } } execv(path, const_cast<char**>(argv)); std::cout << "Intermediate process: Worker failed!" << std::endl; _exit(EXIT_FAILURE); } else if(-1 == workerPid) { std::cout << "Intermediate process: Starting worker failed!" << std::endl; _exit(EXIT_FAILURE); } const pid_t timeoutPid = fork(); if(timeoutPid == 0) { // timeout process std::cout << "Timeout process: Started (" << getpid() << ")." << std::endl; sleep(timeoutInSeconds); std::cout << "Timeout process: Finished." << std::endl; _exit(EXIT_SUCCESS); } else if(-1 == timeoutPid) { std::cout << "Intermediate process: Starting timeout process failed." << std::endl; kill(workerPid, SIGKILL); std::cout << "Intermediate process: Finished." << std::endl; _exit(EXIT_FAILURE); } // --------------------------------------- // This code is only used for double checking if the worker is still running. // The if condition never evaluated to true in my tests. const auto killResult = kill(workerPid, 0); if((-1 == killResult) && (ESRCH == errno)) { std::cout << "Intermediate process: Worker is not running." << std::endl; } // --------------------------------------- std::cout << "Intermediate process: Waiting for child processes." << std::endl; int status = -1; const pid_t exitedPid = wait(&status); // --------------------------------------- // This code is only used for double checking if the worker is still running. // The if condition evaluates to true in the case of an error. const auto killResult2 = kill(workerPid, 0); if((-1 == killResult2) && (ESRCH == errno)) { std::cout << "Intermediate process: Worker is not running." << std::endl; } // --------------------------------------- std::cout << "Intermediate process: Child process finished. Status: " << status << "." << std::endl; if(exitedPid == workerPid) { std::cout << "Intermediate process: Killing timeout process." << std::endl; kill(timeoutPid, SIGKILL); } else { std::cout << "Intermediate process: Killing worker process." << std::endl; kill(workerPid, SIGKILL); std::cout << "Intermediate process: Waiting for worker process to terminate." << std::endl; wait(nullptr); std::cout << "Intermediate process: Finished." << std::endl; _exit(EXIT_FAILURE); } std::cout << "Intermediate process: Waiting for timeout process to terminate." << std::endl; wait(nullptr); std::cout << "Intermediate process: Finished." << std::endl; _exit(checkStatus(status) ? EXIT_SUCCESS : EXIT_FAILURE); } else if(-1 == intermediatePid) { // error std::cout << "Parent process: Error starting intermediate process!" << std::endl; result = false; } else { // parent process std::cout << "Parent process: Intermediate process started. PID: " << intermediatePid << "." << std::endl; processId = intermediatePid; } return(result); } bool waitForProcess(const pid_t processId) { int status = 0; const auto waitResult = waitpid(processId, &status, 0); auto result = false; if(waitResult == processId) { result = checkStatus(status); } return(result); } int main() { pid_t pid = 0; const char* const path = "/bin/ls"; const char* argv[] = { "/bin/ls", "--help", nullptr }; const unsigned int timeoutInS = 5; const auto startResult = startProcess(path, argv, timeoutInS, pid, nullptr); if(startResult) { const auto waitResult = waitForProcess(pid); std::cout << "waitForProcess returned " << waitResult << "." << std::endl; } else { std::cout << "startProcess failed!" << std::endl; } } 

编辑

预期的产出应该包含

• 中级进程：等待subprocess。
• 中级进程：subprocess完成。 状态：0。
• 中级进程：杀死超时进程。

在出错的情况下，输出看起来像这样

• 中级进程：等待subprocess。
• 中级进程：subprocess完成。 状态：-1
• 中间过程：杀死工作进程。

运行示例代码时，您将很可能看到预期的输出。 我不能在一个简单的例子中重现错误的结果。

 #if !defined(_WIN32) && !defined(__SYMBIAN32__) // Ignore SIGPIPE signal, so if browser cancels the request, it // won't kill the whole process. (void) signal(SIGPIPE, SIG_IGN); // Also ignoring SIGCHLD to let the OS to reap zombies properly. (void) signal(SIGCHLD, SIG_IGN); #endif // !_WIN32 

 if(exitedPid == workerPid) {