Java threads and fork concept

[Anil Deshpande]

I just wanted to know what is the comparison of Threads in Java and forking concept in Unix.
As far as I know, correct me if I am wrong

Forking is multiprocessing. When you fork a child process (not thread) get's created. The the child process will not share any resources with the parent process from which it got created through forking.

But this is not the case with the Threads in Java.When you create threads, there share the same process resources.

Am I right? Is it proper to compare the Threads of Java and Fork. Or is it like Apple to Orange comparison. I need some proper perspective about this.

Thanks,

[Campbell Ritchie]

Did this tutorial help at all?

[Winston Gutkowski]

Anil Deshpande wrote:Am I right? Is it proper to compare the Threads of Java and Fork. Or is it like Apple to Orange comparison. I need some proper perspective about this.

I'd definitely look at Campbell's link, but the functional difference is that what a Thread (or Runtime; and I'd advise you to use the latter) does is independent of the Thread that spawned it.

In languages that implement fork() in it's usual form, it spawns an identical process (of some kind, heavy- or lightweight) that continues on from where the fork() was encountered, usually with a copy of all the process state information at that time.

Java Threads, on the other hand, can process code that is entirely different from the Thread that spawned them, but what they usually (and I say this because I'm NOT a Java multi-threading expert) share/clone is the environment of the spawning Thread (current directory, critical variable states ... things like that).

As to details, you really do need to check the tutorials (or the JLS).

HIH

Winston

[Jesper de Jong]

On most modern operating systems, a process is a program running on a computer, that is separate from other processes running on the computer. Each process has its own address space and other resources, and it cannot access the address space and other resources of other processes directly.

When you fork a process the Unix way, what happens is that a second copy of the program starts running, completely separate from the original copy that was running.

Threads are are more lightweight way to do multiprocessing. One process can have multiple threads running at the same time. All threads share the address space and other resources of the process; different threads in the same process can directly access each other's data.

[Winston Gutkowski]

Jesper de Jong wrote:different threads in the same process can directly access each other's data.

Good point. Glad I used Thread, not 'thread'.

Winston

[Anil Deshpande]

thanks a lot.. the tutorial also helped