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Java Forum / General / October 2006File.delete takes time
In windows (not sure about unix) I find that if I iterate through files in a dir and file.delete() each one and at the end of the loop I immediately list the files in the directory, some of the files are still there. Does it take time after the delete for the files to actually go away? Thanks! Aaron Fude > In windows (not sure about unix) I find that if I iterate through files > in a dir and file.delete() each one and at the end of the loop I [quoted text clipped - 6 lines] > > Aaron Fude Had a similar problem some time ago. Calling the garbage collection with System.gc() after the loop before checking should solve this issue. >> In windows (not sure about unix) I find that if I iterate through files >> in a dir and file.delete() each one and at the end of the loop I [quoted text clipped - 7 lines] > Calling the garbage collection with System.gc() after the loop before > checking should solve this issue. Calling System.gc() is rarely a solution for anything. It's not even guaranteed to do anything. I'd guess that it just makes it look like things are working. The real problem is likely to still be lurking somewhere. Dan.  SignatureDaniel Dyer http://www.uncommons.org >>> In windows (not sure about unix) I find that if I iterate through files >>> in a dir and file.delete() each one and at the end of the loop I [quoted text clipped - 12 lines] > things are working. The real problem is likely to still be lurking > somewhere. I'll second that. If System.gc() does occasionally appear to help here, it likely means that you're leaking open file handles somewhere. It may seem convenient to let the garbage collector do your close()ing for you, but it'll introduce serious problems if you try to, say, delete or rename the file that still has an open FileInputStream on it. The exact kind of problem varies by platform, making this one especially fun. SignatureMark Jeffcoat Austin, TX >> In windows (not sure about unix) I find that if I iterate through files >> in a dir and file.delete() each one and at the end of the loop I >> immediately list the files in the directory, some of the files are >> still there. > Calling the garbage collection with System.gc() after the loop before > checking should solve this issue. If a Java object does something (like closing a file) when it is finalized then that action is unpredictably delayed and can cause surprising problems. One I ran into was a DB application that worked fine under light test and soon stopped under load -- it turned out that a SQL query held onto an item of a limited pool in the DB server until garbage collection called the finalizer. The fix was to explicitly close or finalize the query object before leaving the function that used it. Explicitly calling the garbage collector is a good way to detect this class of problem and a bad way to fix it, both because it's expensive and because it isn't guaranteed to do anything -- it's a "suggestion" to the JVM. However, I don't see a finalizer or close() in java.io.File. It would be a significant bug if File's implementation held a system resource like a file handle. Perhaps you are seeing an OS feature? > If a Java object does something (like closing a file) when it is > finalized then that action is unpredictably delayed and can cause [quoted text clipped - 13 lines] > be a significant bug if File's implementation held a system resource > like a file handle. Perhaps you are seeing an OS feature? Sorry for the confusion; I was talking about problems with unclosed FileInputStreams (and similar classes). One idea I stole from Bruce Eckel's _Thinking in Java_ is a way to use the finalizer to detect these problems. You can't reliably use it to close an open stream, or return a resource to a pool, but you can do something like protected void finalize() throws Throwable { assert(!resource.open()); } in hopes of finding a place where you've broken the rules. (I say hope because, of course, there's no guarantee that the garbage collector will ever even run. This is a check, not an excuse to stop paying attention.) SignatureMark Jeffcoat Austin, TX > In windows (not sure about unix) I find that if I iterate through files > in a dir and file.delete() each one and at the end of the loop I > immediately list the files in the directory, some of the files are > still there. > > Does it take time after the delete for the files to actually go away? Did you check the return value of the delete method? It returns a boolean indicating whether the delete was successful or not. Dan. SignatureDaniel Dyer http://www.uncommons.org 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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