Parallel For

[torial]

I was thinking a default implementation of this (perhaps in CobraCore) , might be a nice buzz line

http://coding-time.blogspot.com/2008/03 ... -in-c.html

[Charles]

Looks interesting. At the very least it could be added to our existing set of threading examples.

[hopscc]

Heres a translation of the article code to cobra

"""
ParallelFor in cobra from <!-- m --><a class="postlink" href="http://coding-time.blogspot.com/2008/03/implement-your-own-parallelfor-in-c.html">http://coding-time.blogspot.com/2008/03 ... -in-c.html</a><!-- m -->
"""
use System.Threading

sig ForDelegate(i as int)
sig ThreadDelegate

class Parallel
    """
        Parallel for loop. Invokes given action, passing arguments
        fromInclusive - toExclusive on multiple threads.
        Returns when loop finished.
    """
    
    def for(fromInclusive as int, toExclusive as int, action as ForDelegate) is shared
        """
        ChunkSize = 1 makes items to be processed in order.
        Bigger chunk size should reduce lock waiting time and thus increase paralelism.
        """ 
        chunkSize = 4    # number of process() threads
        threadCount = Environment.processorCount
        cnt = fromInclusive - chunkSize
 
        # processing function
        # takes next chunk and processes it using action
        process as ThreadDelegate = do
            while true
                cntMem = 0
                lock Parallel.getType
                    # take next chunk
                    cnt += chunkSize
                    cntMem = cnt

                    # process chunk
                    # here items can come out of order if chunkSize > 1
                    for i in cntMem : cntMem + chunkSize
                        if i >=  toExclusive, break
                        action(i)
 

        # launch process() threads
        asyncResults = IAsyncResult[](threadCount)
        for i in 0 : threadCount
            asyncResults[i] = process.beginInvoke(nil, nil)  # line 45

        # wait for all threads to complete
        for i in 0 : threadCount
            process.endInvoke(asyncResults[i])  # line 49
        
    
    def main is shared
        Parallel.for(0, 100, do(i as int))
            # Your parallel code
            Thread.sleep(100)
            Console.writeLine(i)

The only problem is it fails to compile

Code: Select all

parallelFor.cobra(45): error: Cannot find a definition for "beginInvoke" in "process" whose type is "ThreadDelegate". There is a member named ".invoke" with a similar name.
parallelFor.cobra(49): error: Cannot find a definition for "endInvoke" in "process" whose type is "ThreadDelegate". There is a member named ".invoke" with a similar name.
Compilation failed - 2 errors, 0 warnings


I think I've got a correct translation ( but I could be wrong about that)
skim reading delegates seems to indicate .beginInvoke and .endInvoke are added by the Compiler/CLR.
Is it possible/likely that cobra is not aware of that?

[Charles]

Looks like Cobra is not picking up on those methods for delegates. You can fill out a ticket (and even fix if you like). In the meantime you may be able to use sharp'blah blah' to workaround the problem.

[hopscc]

Reported on ticket:196.

Are there any existing handlers/examples in the cobra compiler (method discovery) where it currently has to
add/insert methods that aren't discoverable by inspecting the assemblies ?

[hopscc]

For the above code a workaround using sharp'...' looks like this:
line 45

#asyncResults[i] = process.beginInvoke(nil, nil)
asyncResults[i] = sharp'process.BeginInvoke(null, null)'

line 49

#process.endInvoke(asyncResults[i])
sharp'process.EndInvoke(asyncResults[i])'

[Charles]

Reported on ticket:196.

Are there any existing handlers/examples in the cobra compiler (method discovery) where it currently has to
add/insert methods that aren't discoverable by inspecting the assemblies ?

Not that come to mind. But Cobra often models delegates with a special internal type called MethodSig and that could be the source of the problem.

[hopscc]

Patch available for this on the ticket (ticket:196)