java-ProcessBuilder will not stop

I'm trying to decode an mp3 file to a wav file using the ProcessBuilder class under Linux. For some reason the process doesn't stop, so I have to cancel it manually.

Can someone give me a hint. I think the quoted code is easy to reproduce:

import java.io.*;public class Test { public static void main(String[] args) { try { Process lameProcess = new ProcessBuilder("lame","--decode","test.mp3","-").start(); InputStream is = lameProcess.getInputStream(); FileOutputStream fileOutput = new FileOutputStream("test.wav"); DataOutputStream dataOutput = new DataOutputStream(fileOutput); byte[] buf = new byte[32 * 1024]; int nRead = 0; int counter = 0; while((nRead = is.read(buf)) != -1) { dataOutput.write(buf, 0, buf.length); } is.close(); fileOutput.close(); } catch (Exception e) { e.printStackTrace(); } }}

output of jstack

"main"prio=10 tid=0x0000000002588800 nid=0x247a runnable [0x00007f17e2761000] java.lang.Thread.State: RUNNABLE at java.io.FileInputStream.readBytes(Native Method) at java.io.FileInputStream.read(FileInputStream.java:236) at java.io.BufferedInputStream.fill(BufferedInputStream.java:235) at java.io.BufferedInputStream.read1(BufferedInputStream.java:275) at java.io.BufferedInputStream.read(BufferedInputStream.java:334) - locked(a java.io.BufferedInputStream) at java.io.FilterInputStream.read(FilterInputStream.java:107) at Test.main(Test.java:17)

Solution:

You need to empty the process's output (via getInputStream() ) and error (via getErrorStream() ) streams, otherwise it may block.

Quoting the Process documentation:

Because some native platforms only provide limited buffer size for standard input and output streams, failure to promptly write the input stream or read the output stream of the subprocess may cause the subprocess to block, and even deadlock.

(applies to error streams and output streams)

You may need to drain each stream in a different thread, as each stream may block when there is no data.

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java-ProcessBuilder will not stop

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