Simulating threads scheduling in java (stackless java?)

Question

For some academic research I need to simulate several threads running on a single processor.

I want to be able to insert *call_scheduler()* calls inside my code, in which the current "thread" will pause (remembering in which code line it is) and some scheduling function will decide which thread to let go.

In python, this could be implemented neatly using stackless python. Is there a java alternative?

I could implement it using real threads and some messaging queues (or pipes) that will force only one thread to run at a time - but this is an ugly and problematic solution.

I think there is no explicit way to do this in java, you have to just write some lines of code & you can use semaphores & priority queues — Ehsan Khodarahmi
– Ehsan Khodarahmi, Commented Jun 16, 2012 at 17:52

francesc · Accepted Answer · 2012-07-01 18:06:36Z

1

For cooperative user threads you could use Apache javaflow continuations: http://commons.apache.org/sandbox/javaflow/

I'd be interested in knowing how to implement a preemptive scheduler with this continuations package

answered Jul 1, 2012 at 18:06

francesc

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Konstantin Solomatov · Accepted Answer · 2012-07-01 18:18:55Z

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Scala actors framework like Akka do this. Each thread handles many actors that's how they created so efficiently. I recommend taking look at their source code.

answered Jul 1, 2012 at 18:18

Konstantin Solomatov

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Kumar Vivek Mitra · Accepted Answer · 2012-06-16 17:49:50Z

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Your question:

I could implement it using real threads and some messaging queues (or pipes) that will force only one thread to run at a time - but this is an ugly and problematic solution

Well if you want only a single thread to run at a time, by controlling the access of the thread on the object in a cleaner way, then use the Semaphores in java.util.concurrent package.

Semaphores sem = new Semaphores(1); // 1 here will mark that only one thread can have access

use sem.acquire() to get the key of the object, and when its done, use sem.release() then only another thread will get the access to this object.

answered Jun 16, 2012 at 17:49

Kumar Vivek Mitra

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7 Comments

Oren Over a year ago

But I want to be able to control from the scheduler-thread which thread will continue - so I'll need an array of semaphores, one for every thread.

Kumar Vivek Mitra Over a year ago

create an HashMap of semaphores, so u can identify them by their keys, like first_thread, second_thread...etc

Oren Over a year ago

Is the native scheduler smart enough to understand that all the threads are waiting for the semaphore and only one thread can be active - so there is no reason to pause it?

Oren Over a year ago

Kumar Vivek Mitra - what's wrong with a unique index for every thread and an array?

Kumar Vivek Mitra Over a year ago

using the new concurrent package, u can be assured of Thread Safety, thats it.... its just like if you want thread safety use StringBuffer class, else use StringBuilder..same difference here.

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