Sequential execution of java programs == sequential activation of the jvm ?

Question

Hi....

I've a bash script that sequentially calls a java program. That's a bit tricky but mainly what i do is to have a loop and executes about 1500 times the same java program with different arguments.

My question is, when using java 1.5 (the sun VM), each time I'm calling the java program a new instance of the jvm is created ? (I'm not sure that's the right vocabulary...)

Should I avoid this situation by introducing a level of indirection, i.e building a list of all the parameters and then executing one java program which takes these parameters and executes what was previously my entry point ?

Or can I deal with the problem by configuring the JVM as resident or something like that and dynamically invokes my program....

hope this is clear....

thx...

Answer 1

You could save the parameters into a file and use the Java program to process it without constant restart. You could also pipe in the parameters into the running Java app through the console, similarly as for example ls | grep java

Edit: And for the first question. I doubt the java runtime would stay deliberately in memory. Probably most JRE files would remain in the disk cache anyway. On Windows there is a Java Quick Start service which keeps the JRE files around to reduce the startup time for a java program. Don't know whether there is a similar thing for *nix.

Answer 2

Obviously having all the parameters beforehand and running the program once after that would be the best solution. If you cannot do that for any reason i have a very dirty solution to this. Have your program register a port and listen to it for input. Then simply pass the arguments to that port and have your program handle them as a new instance.

Answer 3

JVM startup is notoriously slow, and it certainly not intended to be done in a loop like that. Unfortunately the only way to avoid this if you are passing command line parameters to the java program is to modify the java program itself in some way to have alternative forms of interaction (either from the console, or a port, or a read a file). Java Quick Start is the only (closest thing to a) solution if the java program cannot be changed.

The real solution is to change the Java program. The most obvious change would be to have your loop write to a file, and then start the java program that would read the file one line at a time. That works if the loop doesn't care about the results from the java program for the next set of parameters.

If it does, then it would really be necessary to understand that relationship to advise on an appropriate solution. The socket solution suggested by Savvas is certain a general purpose solution, but there may be better options, depending on what you need to accomplish.