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我用這個answer啓發了一個使用fork（）和execv（）啓動進程的輔助函數。它用於例如開始mysqldump進行數據庫備份。 該代碼在不同程序的幾個不同位置完全正常工作。Linux：fork＆execv，等待子進程掛起
現在我打了一個失敗的星座： 這是一個調用systemctl來停止一個單位。運行systemctl工作，單元停止。但是在中間進程中，當wait（）等待子進程時，wait（）會掛起，直到超時過程結束。 如果我檢查，如果工作進程完成kill（），我可以告訴它它已經完成。
重要提示：除了wait（）不表示結束工作進程外，程序不會發生錯誤或故障。 我的代碼中是否有任何內容（見下文）不正確，可能會觸發該行爲？ 我讀過Threads and fork(): think twice before mixing them，但我找不到與我的問題有關的任何內容。
奇怪的是： 程序中使用了深入深入的JSON-RPC。如果我使用JSON-RPC停用代碼，那麼一切正常！？
環境： 使用該函數的程序是一個多線程應用程序。所有線程的信號都被阻止。主線程通過sigtimedwait（）處理信號。
代碼（生產代碼，其中測井得到通過的std :: COUT交易來輸出）與樣品主要功能：
#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;
}
}
編輯
預期的輸出應包含
- 中間過程：等待子過程。
- 中間過程：子過程完成。狀態：0.
- 中間過程：殺死超時過程。
在錯誤的情況下輸出看起來像這樣
- 中間過程：等待子進程。
- 中間過程：子過程完成。狀態：-1
- 中間過程：殺死工作進程。
當您運行示例代碼時，您很可能會看到預期的輸出。我不能在一個簡單的例子中重現錯誤的結果。
而父被阻止'wait'，請問孩子顯示爲一個殭屍？ – Useless
我編譯和運行的代碼，我沒覺得有有奇怪的行爲，你能提供的'預期result'和'當前result'？ –
@無用：沒有殭屍進程。 'ps -l'返回例如用於中間的進程ID 617，用於超時的進程ID 619，但不是618。 我在殺碼測試（）產生相同的結果。 – DrP3pp3r