Introducing CLIPC

The Short Story

CLIPC is a new open-source java library for IPC. It provides new IPC primitives like semaphores and shared queues, and it makes existing primitives like shared memory easier to use. CLIPC currently supports the Windows and Linux platforms.

The Long Story

CLIPC is the com.lts.ipc library that I wrote because I could not find a Java library that did some Inter-Process Communications (IPC) functions that I was interested in. CLIPC has been the topic of several talks that I have given recently at the Boulder Java Users Group (BJUG) and the Denver Open Source Users Group (DOSUG).

Over the next couple of weeks, I am hoping to create some blog entries about CLIPC and some of the trials and tribulations I went through to write the library. This will be of interest to people who are interested in IPC and also those are are interested in the Java Native Interface (JNI).

CLIPC makes use of JNI because Java does not support certain IPC concepts like Semaphores and FIFOs. This requires the use of JNI to perform the required system calls and whatnot through C, a language that the two platforms that CLIPC currently supports uses.

Another aspect of CLIPC/JNI is that it requires the creation of a consistent interface across multiple platforms. Both Windows and Linux support First-In, First-Out messaging (FIFOs), but the similarities pretty much end there.

For example, on Windows there are Named Pipes. These are always bi-directionaly and function in a lot of ways like very fast TCP/IP connections. Named pipes are represented with files in a special directory.

Linux also supports FIFOs, but on that platform they are uni-directional. They appear to be files on the file system in that there are no naming requirements and they can appear anywhere that regular files can. Linux FIFOs require no special system calls in order to connect to, though they do require special calls to create.

How do you reconcile these differences in order to create a uniform interface to FIFOs? Should they really be more like the named pipes of Windows and allow bi-directional data flow or should they be uni-directional?

I don't know if I made the best decisions possible for CLIPC, but I can talk about why I made the decisions that I did. This will be the topic of future blog entries.