After having some time to think about what I wrote yesterday I too realized that the conclusion one can draw from the matrix multiplication example is different: "Don't parallelize communication heavy algorithms". Still, it shows that the sharing has its costs (as you too point out). One result from Marcs tests was that the Coro implementation running on one core was 25-35% faster with a perl without ithread support. I.e. everyone with a standard perl installation is paying this price with or without using threads.

It is (all but) impossible to parallelise matrix multiplication using "real processes" alone

I don't think so. If you can afford 4 times the memory usage a process implementation will be nearly 4 times faster on a quad-core. Every process uses its own non-shared memory to calculate one fourth of the rows.

Marc Lehmann achieves his results by using threads. Albeit that they are a user space implementation of cooperative threading, it is still threading ...

Now we've established that a form of threading is required!

Note that his Coro threads don't have any parallelization potential for multi-cores. They should run exactly the same on one core vs. a quad-core. He could have used a simple non-threaded matrix-multiplication and it would have run exactly the same. His Coro threads have two uses as I see it: Making it easier to program independent tasks in a program and speeding up programs where I/O, user input etc. provide opportunities for parallel tasks. They don't help with multi-cores at all

This is the reason Marc Lehmann only used a single core to benchmark his Coro-implementation. And therefore your conclusion is wrong. Threads are not required

To answer your question about the code, his implementation of the benchmark can be found at http://data.plan9.de/matmult. Please check it out, I will try to do it tonight when I have some time.

In reply to Re^5: If I am tied to a db and I join a thread, program chrashes by jethro
in thread If I am tied to a db and I join a thread, program chrashes by lance0r

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