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Java Forum / Virtual Machine / September 2004jvm and pipes problem
Hi all, I have a java program that open some threads (not too many. around 15-20 threads). Sometimes I get the following exception: java.io.IOException: Too many open files at java.lang.UNIXProcess.forkAndExec(Native Method) at java.lang.UNIXProcess.<init>(UNIXProcess.java:54) at java.lang.Runtime.execInternal(Native Method) at java.lang.Runtime.exec(Runtime.java:566) at java.lang.Runtime.exec(Runtime.java:428) at java.lang.Runtime.exec(Runtime.java:364) at java.lang.Runtime.exec(Runtime.java:326) So I used lsof and I discovered that I have hundreds of pipes. I have hundreds of lines similar to the following: java 18732 boazy 21u FIFO 0x30007b52908 0t0 263566 (fifofs) PIPE->0x30007b52820 My questions are: 1. What are those pipes? How does the jvm uses them? 2. When does the jvm closes those pipes? 3. Is it possible that I have pipes leak? 4. How do I solve my problem? I use java 1.4.1_02-b06 and Solaris 2.8 I'll be greatful for any related information that will help me understand and solve the problem. Thanks, Boaz. > I have a java program that open some threads (not too many. around > 15-20 threads). Sometimes I get the following exception: > > java.io.IOException: Too many open files [...] > My questions are: > 1. What are those pipes? How does the jvm uses them? > 2. When does the jvm closes those pipes? > 3. Is it possible that I have pipes leak? > 4. How do I solve my problem? You've been using Runtime.exec() and not cleaning up the files it opens. Each time you call Runtime.exec() to create a child process, the JVM creates three pipes connecting the stdin, stdout and stderr of the child to the corresponding streams available from the Process object returned by Runtime.exec(). You need to close those three streams after the child has terminated. /gordon  Signature[ do not email me copies of your followups ] g o r d o n + n e w s @ b a l d e r 1 3 . s e > Each time you call Runtime.exec() to create a child process, the JVM > creates three pipes connecting the stdin, stdout and stderr of the > child to the corresponding streams available from the Process object > returned by Runtime.exec(). > > You need to close those three streams after the child has terminated. this means, those streams won't be closed in the finalizer? does Process.destroy() close them? (how/where would i find out myself next time...) andreas > this means, those streams won't be closed in the finalizer? does > Process.destroy() close them? (how/where would i find out myself > next time...) Most likely they *will* be closed eventually, when the correspoding streams are finalized. You can look at the source code for the relevant classes just as well as I can, it's packaged with the JDK. In some cases you might need the complete JDK source package from http://developer.sun.com/ . However you should never rely on the garbage collector for collecting "external" resources like file descriptors, at least not in any timely manner. If a class provides a method for the explicit purpose of closing or releasing it, then you should use it. IMO it's bad style to rely on the garbage collector to do it for you if methods are available. For one thing, gc doesn't even know about open file descriptors. Remember that it's lack of memory, not lack of file descriptors that triggers gc. Since file descriptors are a much scarcer resource than memory, you will most likely run out of them long before memory is low. In fact, you already did. On the other hand, the Process class itself should probably close the streams as soon as the reaper thread cleans up after the terminated child process. In particular you shouldn't be forced to close them if you never used them in the first place, as is often the case. /gordon Signature[ do not email me copies of your followups ] g o r d o n + n e w s @ b a l d e r 1 3 . s e > You've been using Runtime.exec() and not cleaning up the files it > opens. [quoted text clipped - 7 lines] > > /gordon Thanks for the quick response. How do I "close those three streams": 1. Can I use Process.destroy()? does it has effect after the child terminated? 2. If I wait for the thread that called the Runtime.exec() to finish (and also other threads that have a refernece to the Process), will it close the streams? 3. If I use getInputStream(), for example, and then call the close() method, does that do the job (I will do that of course for all the 3)? Thanks again, Boaz. > How do I "close those three streams": > 1. Can I use Process.destroy()? does it has effect after the child > terminated? No. > 2. If I wait for the thread that called the Runtime.exec() to finish > (and also other threads that have a refernece to the Process), will it > close the streams? No. > 3. If I use getInputStream(), for example, and then call the close() > method, does that do the job (I will do that of course for all the 3)? Yes, "get" each of the streams (input, output, error) and call its close() method. /gordon Signature[ do not email me copies of your followups ] g o r d o n + n e w s @ b a l d e r 1 3 . s e Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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