使用 waitUntilExit 挂起 NSTask

Question

我需要同步使用 NSTask，但是我发现有时我的任务会在“waitUntilExit”命令下挂起。我想知道是否有一种优雅的方式——一种错误处理方法——来终止挂起的任务，以便我可以重新启动另一个？

Answer 1

请注意，如果通过NSTask 运行的任务填满了输出管道，那么进程将挂起，从而有效地阻止waitUntilExit 返回。

你可以通过调用来防止这种情况

[task.standardOutput.fileHandleForReading readDataToEndOfFile];

打电话之前

[task waitUntilExit];

这将导致读取输出管道的数据，直到写入输出管道的进程关闭它。

演示问题和各种解决方案的示例代码：

https://github.com/lroathe/PipeTest

Answer 2

您可以使用-[task launch] 启动任务，然后定期轮询其isRunning 属性以检查它是否已经完成。如果在给定的时间间隔后它还没有完成，您可以调用-[task terminate] 来终止它。这要求您启动的任务不会忽略 SIGTERM 信号。

如果在您的情况下轮询任务终止效率太低，您可以在启动任务后设置DISPATCH_SOURCE_TYPE_PROC 类型的调度源。然后，当任务终止时，此源会异步调用其事件块：

dispatch_source_create(DISPATCH_SOURCE_TYPE_PROC, task.processIdentifier, DISPATCH_PROC_EXIT, dispatch_get_main_queue());

Answer 3

这是一个 NSTask 类别，它为您提供了一个对超时友好的 waitUntilExit。它还允许您安排 SIGTERM 和 SIGKILL。

此方法旨在 1) 永远不要无限旋转，以及 2) 确保进程被终止。

@interface NSTask (TRTaskAdditions_termination)

// This method mitigates the infinite-blocking potential of [NSThread waitUntilExit]
//
// Returns a BOOL indicating whether or not the process exited.
// 
// Inputs:
// TO: The initial timeout, during which time we wait for the task to exit. (There are additional timeouts if SENTERM or SENDKILL are YES.
// SENDTERM: If we don't exit during the initial timeout, send SIGTERM and wait 2 seconds.
// SENDKILL: If we still haven't exited, send SIGKILL and wait 2 seconds.
// 
// The method runs as follows:
// Step 1: Poll [self isRunning] for (TO) seconds. If the task stops running during that time, we return immediately with YES
// Step 2: If the task didn't exit after (TO) seconds, we send it a SIGTERM if (SENDTERM == YES). Wait 2 seconds for the task to exit.
// Step 3: If the task exits, return YES. If it _still_ hasn't exited (i.e. it ignored the SIGTERM,) send it a SIGKILL if (SENDKILL == YES).
// Step 4: Wait another 2 seconds for the task to end. If it exits, return YES. Otherwise, if the task is still running, return NO.
//
// In theory, setting SENDKILL to YES should terminate any process. Processes aren't supposed to be able to escape signal #9 (KILL).
- (BOOL)waitUntilExitWithTimeout:(CFTimeInterval)TO sendTerm:(BOOL)SENDTERM sendKill:(BOOL)SENDKILL;

@end



#include <signal.h>

@implementation NSTask (TRTaskAdditions_termination)

- (BOOL)waitUntilExitWithTimeout:(CFTimeInterval)TO sendTerm:(BOOL)SENDTERM sendKill:(BOOL)SENDKILL
{
    CFAbsoluteTime      started;
    CFAbsoluteTime      passed;
    BOOL                exited = NO;

    started = CFAbsoluteTimeGetCurrent();
    for (
         CFAbsoluteTime now = started;
         !exited && ((passed = now - started) < TO);
         now = CFAbsoluteTimeGetCurrent()
         )
    {
        if (![self isRunning])
        {
            exited = YES;
        } else {

            CFAbsoluteTime sleepTime = 0.1;
            useconds_t sleepUsec = round(sleepTime * 1000000.0);
            if (sleepUsec == 0) sleepUsec = 1;
            usleep(sleepUsec); // sleep for 0.1 sec

        }
    }

    if (!exited)
    {
        //NSLog(@"%@ didn't exit after timeout of %0.2f sec", self, TO);

        if (SENDTERM)
        {
            TO = 2; // 2 second timeout, waiting for SIGTERM to kill process

            //NSLog(@"%@ sending SIGTERM", self);
            [self terminate];
            /* // UNIX way
             pid_t pid = [self processIdentifier];
             kill(pid, SIGTERM);
             */

            started = CFAbsoluteTimeGetCurrent();
            for (
                 CFAbsoluteTime now = started;
                 !exited && ((passed = now - started) < TO);
                 now = CFAbsoluteTimeGetCurrent()
                 )
            {
                if (![self isRunning])
                {
                    exited = YES;
                } else {
                    usleep(100000);
                }
            }
        }

        if (!exited && SENDKILL)
        {
            TO = 2; // 2 second timeout, waiting for SIGKILL to kill process

            //NSLog(@"%@ sending SIGKILL", self);
            pid_t pid = [self processIdentifier];
            kill(pid, SIGKILL);

            started = CFAbsoluteTimeGetCurrent();
            for (
                 CFAbsoluteTime now = started;
                 !exited && ((passed = now - started) < TO);
                 now = CFAbsoluteTimeGetCurrent()
                 )
            {
                if (![self isRunning])
                {
                    exited = YES;
                } else {
                    usleep(100000); // sleep for 0.1 sec
                }
            }
        }
    }

    return exited;
}

@end