Question

我已经在网上搜索了，问题process.waitFor() never returns表明进程通常是stdout或stderr无法读取的问题。

我们使用ProcessBuilder与redirectOutput和redirectError来实现此目标，我认为我们应该安全，请参阅我们用于执行流程的以下方法：

public static void execute(String directory, long timeout, File out, File err, String... command) throws InterruptedException, IOException {
    LOGGER.log(Level.INFO, String.format("executing command %s (%s)", Arrays.toString(command), timeout > 0 ? String.format("timeout = %,d[ms]", timeout) : "no timeout"));
    ProcessBuilder builder = new ProcessBuilder();
    builder.directory(new File(directory));
    builder.command(command);
    builder.redirectOutput(out);
    if(out == err) {
        builder.redirectErrorStream(true);          
    } else {
        builder.redirectError(err);
    }
    long time = System.currentTimeMillis();
    Process process = builder.start();
    try {
        LOGGER.log(Level.FINE, "waiting for process");
        boolean exited = process.waitFor(timeout, TimeUnit.MILLISECONDS);
        if(!exited) {
            LOGGER.log(Level.WARNING, "timeout reached, trying to destroy ...");
            exited = destroy(silent, process); // Helper method to destroy processes
        }
        long duration = System.currentTimeMillis() - time;
        int exitValue = process.exitValue();
        LOGGER.log(Level.INFO, "execution finished in " + duration + "[ms] => " + exitValue);
    } catch (InterruptedException | Error | RuntimeException e) {
        LOGGER.log(Level.SEVERE, "execution failed", e);
        throw e;
    }
}

然而，问题是它挂在process.waitFor(timeout, TimeUnit.MILLISECONDS)调用上，即使该进程很容易在超时内完成。

日志记录输出

Oct 07, 2017 12:39:55 AM at.ProcessExecutor execute
INFO: executing command [java, -Xmx8G, -XX:+UseG1GC, -XX:+CrashOnOutOfMemoryError, -jar, MetricCalc.jar] (timeout = 14,400,000[ms])
Oct 07, 2017 12:39:55 AM at.ProcessExecutor execute
FINE: waiting for process

（认识到尚未编写execution finished行）

err文件读取

... Things we write to std.err ...
Finished Metrics

并且MetricCalc的主要方法看起来像

public static void main(String[] args) {
    .... do some stuff ...
    System.err.println("Finished Metrics");
}

表示读取工作正常，Java程序的最后一行已经执行，进程应该已经终止。

任何人都知道为什么流程没有终止/它仍然挂在Process.waitFor()上？

Answer 1

这不是Process.waitFor()的问题，而是流程终止的问题。

开始使用的java应用程序使用了ExecutorService没有正确击落并使僵尸线程保持活动状态，这阻止了进程终止。

添加executorService.shutdown()解决了问题，应用程序现在按预期终止。

即使stdout和stderr被读取，Process.waitFor也会挂起

1 个答案: