Re: namepipe
- From: Ben Phillips <b.phillips@xxxxxxxxxxxxxxxxx>
- Date: Sat, 22 Sep 2007 02:01:33 -0400
timothy ma and constance lee wrote:
Sir
I got a problem:
Program A need to wirte a file and then program B will use that file after Program A release the lock of the file.
I think i may use namepipe in C but how about if using java. Any other good suggestion?
A lot of problems that are best solved in C by using multiple processes communicating are, in Java, better solved by using multiple threads inside of a single JVM process. In this instance, one just has a producer/consumer pattern with a stream-like object that has a synchronized put and get of some sort. The java.util classes provide implementations of Deque, Stack, and Queue that you might synchronize on and use for inter-thread communication (e.g. a job queue). For a character stream, use a Stream you make that looks like an input stream to one thread and an output stream to the other, with the input stream read methods blocking until the other thread writes to the output stream interface of the object, and synchronization used. Read up on synchronization, Object.wait(), Object.notify(), and then check up on java.util.concurrent. Synchronization and other threading matters are covered in Sun's Java tutorials at java.sun.com and wait, notify, Deque, Stream, and the like have in-depth javadocs ("synchronized" itself doesn't as it's a language keyword, though). Packages of interest: java.util, java.util.concurrent, java.lang (Object and Thread, and various exceptions), and java.io (streams).
If you must go with interprocess communication, streams are again the way to go, but you'll have no simple and reliable file locking mechanism from in Java (at least without resorting to JNI). If the host operating system provides an atomic nonexistent-file-creation shell command you can System.exec this to atomically create lockfiles with a failure return if the lockfile's already been created by another process, and implement cooperative locking in the manner typical on Unix systems. You might also want to look into RMI and other such complicated file-less methods of Java interprocess communication, or replace using a file with using a database that maintains transactional integrity with concurrent uses (you get an atomic lock-creation primitive, at minimum, since any DBMS worth even its weight in cat turds will provide atomic transactions in general).
You may even be able to use System.exec from one process to create the other and pipe an OutputStream to the new process's input; check the System and ProcessBuilder javadocs and experiment to see if you can get a simple demo working.
But your best bet is probably with turning these processes into threads and sharing a data structure such as a queue. C provides no standard threading or internal synchronization tools, which results in the C idiom being IPC with external files, named pipes, lockfiles, and the like. Java does provide standard threading and synchronization tools.
.
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