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From "Nickolay Martinov (JIRA)" <j...@apache.org>
Subject [jira] Created: (EXEC-57) DefaultExecutor.execute() does not return even if child process terminated
Date Sat, 26 Feb 2011 11:47:21 GMT
DefaultExecutor.execute() does not return even if child process terminated
--------------------------------------------------------------------------

                 Key: EXEC-57
                 URL: https://issues.apache.org/jira/browse/EXEC-57
             Project: Commons Exec
          Issue Type: Bug
    Affects Versions: 1.1
         Environment: > uname -smr
HP-UX B.11.23 ia64

$ uname -smr
Linux 2.6.18-194.3.1.el5xen x86_64


            Reporter: Nickolay Martinov


When script that starts background process is synchronously executed via DefaultExecutor.execute()
then method never returns (until child process spawned by child process terminates).

Here is example if such script:

echo "Going to start daemon process"
sleep 1
cd ./target
nohup sleep 10 &
sleep 1
echo "Daemon process was started"

Stream handler is used to grab and print output of script. As can be seen from stack trace
problem lies in pump threads that call InputStream.read() that does not return when script
that we invoke terminates. Instead it returns only once process started by script terminates.


"Thread-3" daemon prio=10 tid=00c73a00 nid=17 lwp_id=2640638 runnable [2e180000]
   java.lang.Thread.State: RUNNABLE
        at java.io.FileInputStream.readBytes(Native Method)
        at java.io.FileInputStream.read(FileInputStream.java:177)
        at java.lang.UNIXProcess$DeferredCloseInputStream.read(UNIXProcess.java:313)
        at org.apache.commons.exec.StreamPumper.run(StreamPumper.java:105)
        at java.lang.Thread.run(Thread.java:662)

   Locked ownable synchronizers:
        - None

"Thread-2" daemon prio=10 tid=005fd000 nid=16 lwp_id=2640637 runnable [2e240000]
   java.lang.Thread.State: RUNNABLE
        at java.io.FileInputStream.readBytes(Native Method)
        at java.io.FileInputStream.read(FileInputStream.java:199)
        at java.lang.UNIXProcess$DeferredCloseInputStream.read(UNIXProcess.java:322)
        at java.io.BufferedInputStream.fill(BufferedInputStream.java:218)
        at java.io.BufferedInputStream.read1(BufferedInputStream.java:258)
        at java.io.BufferedInputStream.read(BufferedInputStream.java:317)
        - locked <628b1970> (a java.io.BufferedInputStream)
        at java.io.FilterInputStream.read(FilterInputStream.java:90)
        at org.apache.commons.exec.StreamPumper.run(StreamPumper.java:105)
        at java.lang.Thread.run(Thread.java:662)

   Locked ownable synchronizers:
        - None

"main" prio=10 tid=0046aa00 nid=1 lwp_id=-1 in Object.wait() [7fff8000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <627e4968> (a java.lang.Thread)
        at java.lang.Thread.join(Thread.java:1186)
        - locked <627e4968> (a java.lang.Thread)
        at java.lang.Thread.join(Thread.java:1239)
        at org.apache.commons.exec.PumpStreamHandler.stop(PumpStreamHandler.java:171)
        at org.apache.commons.exec.DefaultExecutor.executeInternal(DefaultExecutor.java:363)
        at org.apache.commons.exec.DefaultExecutor.execute(DefaultExecutor.java:160)
        at org.apache.commons.exec.DefaultExecutor.execute(DefaultExecutor.java:147)

I added timeout to join() and call interrupt() but that doesnt help to kill pump threads.
Fortunately, these are daemon threads that do not block JVM from exiting. Except from extra
daemon threads this solved problem on linux. But that wasnt able to prevent all hangs on HP-UX.
Check following stack

"main" prio=10 tid=00465600 nid=1 lwp_id=-1 runnable [7fffd000]
   java.lang.Thread.State: RUNNABLE
        at java.io.FileInputStream.close0(Native Method)
        at java.io.FileInputStream.close(FileInputStream.java:259)
        at java.lang.UNIXProcess$DeferredCloseInputStream.close(UNIXProcess.java:298)
        at java.io.BufferedInputStream.close(BufferedInputStream.java:451)
        at org.apache.commons.exec.DefaultExecutor.closeStreams(DefaultExecutor.java:281)
        at org.apache.commons.exec.DefaultExecutor.executeInternal(DefaultExecutor.java:364)
        at org.apache.commons.exec.DefaultExecutor.execute(DefaultExecutor.java:160)
        at org.apache.commons.exec.DefaultExecutor.execute(DefaultExecutor.java:147)
        at org.apache.commons.exec.DefaultExecutorTest.testSyncInvocationOfBackgroundProcess(DefaultExecutorTest.java:812)

I dont have idea how this can be interrupted or timed out except that skip closing streams.
But in this case we'll probably leak resources.

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