source: libcfa/src/executor.cfa @ bf4fe05

// Mutex buffer is embedded in the nomutex executor to allow the executor to delete the workers without causing a
// deadlock.  If the executor is the monitor and the buffer is class, the thread calling the executor's destructor
// (which is mutex) blocks when deleting the workers, preventing outstanding workers from calling remove to drain the
// buffer.

#include <thread.hfa>
#include <collections/list.hfa>

forall( T &, TLink& = dlink(T) | embedded(T, TLink, dlink(T)) ) {
        monitor Buffer {                                                                        // unbounded buffer
                dlist( T, TLink ) queue;                                                // unbounded list of work requests
                condition delay;
        }; // Buffer

        void insert( Buffer(T, TLink) & mutex buf, T * elem ) with(buf) {
                dlist( T, TLink ) * qptr = &queue;                              // workaround https://cforall.uwaterloo.ca/trac/ticket/166
                insert_last( *qptr, *elem );                                    // insert element into buffer
                signal( delay );                                                                // restart
        } // insert

        T * remove( Buffer(T, TLink) & mutex buf ) with(buf) {
                dlist( T, TLink ) * qptr = &queue;                              // workaround https://cforall.uwaterloo.ca/trac/ticket/166
                // if ( (*qptr)`isEmpty ) wait( delay );                // no request to process ? => wait
          if ( (*qptr)`isEmpty ) return 0p;                                     // no request to process ? => wait
                return &try_pop_front( *qptr );
        } // remove
} // forall

struct WRequest {                                                                               // client request, no return
        void (* action)( void );
        inline dlink(WRequest);
}; // WRequest
P9_EMBEDDED(WRequest, dlink(WRequest))

void ?{}( WRequest & req ) with(req) { action = 0; }
void ?{}( WRequest & req, void (* action)( void ) ) with(req) { req.action = action; }
bool stop( WRequest & req ) { return req.action == 0; }
void doit( WRequest & req ) { req.action(); }

// Each worker has its own set (when requests buffers > workers) of work buffers to reduce contention between client
// and server, where work requests arrive and are distributed into buffers in a roughly round-robin order.

thread Worker {
        Buffer(WRequest) * requests;
        WRequest * request;
        unsigned int start, range;
}; // Worker

void main( Worker & w ) with(w) {
        for ( int i = 0;; i = (i + 1) % range ) {
                request = remove( requests[i + start] );
          if ( ! request ) { yield(); continue; }
          if ( stop( *request ) ) break;
                doit( *request );
                delete( request );
        } // for
} // Worker::main

void ?{}( Worker & worker, cluster * wc, Buffer(WRequest) * requests, unsigned int start, unsigned int range ) {
        ((thread &)worker){ *wc };
        worker.[requests, request, start, range] = [requests, 0p, start, range];
} // ?{}

WRequest * current_request( Worker & worker ) { return worker.request; }

struct Executor {
        cluster * cluster;                                                                      // if workers execute on separate cluster
        processor ** processors;                                                        // array of virtual processors adding parallelism for workers
        Buffer(WRequest) * requests;                                            // list of work requests
        Worker ** workers;                                                                      // array of workers executing work requests
        unsigned int nprocessors, nworkers, nrqueues;           // number of processors/threads/request queues
        bool sepClus;                                                                           // use same or separate cluster for executor
        unsigned int next;                                                                      // demultiplexed across worker buffers
}; // Executor

unsigned int tickets( Executor & ex ) with(ex) {
        //return uFetchAdd( next, 1 ) % nrqueues;
        return next++ % nrqueues;                                                       // no locking, interference randomizes
} // tickets

void ?{}( Executor & ex, unsigned int np, unsigned int nw, unsigned int nr, bool sc = false ) with(ex) {
        [nprocessors, nworkers, nrqueues, sepClus] = [np, nw, nr, sc];
        assert( nrqueues >= nworkers );
        cluster = sepClus ? new( "Executor" ) : active_cluster();
        processors = aalloc( nprocessors );
        requests = anew( nrqueues );
        workers = aalloc( nworkers );

        for ( i; nprocessors ) {
                processors[i] = new( *cluster );
        } // for

        unsigned int reqPerWorker = nrqueues / nworkers, extras = nrqueues % nworkers;
//      for ( unsigned int i = 0, start = 0, range; i < nworkers; i += 1, start += range ) {
    for ( i; nworkers : start; 0u ~ @ ~ range : range; ) {
            range = reqPerWorker + ( i < extras ? 1 : 0 );
                workers[i] = new( cluster, requests, start, range );
        } // for
} // ?{}

void ?{}( Executor & ex, unsigned int nprocessors, unsigned int nworkers, bool sepClus = false ) {
        ex{ nprocessors, nworkers, nworkers, sepClus };
}
void ?{}( Executor & ex, unsigned int nprocessors, bool sepClus = false ) {
        ex{ nprocessors, nprocessors, nprocessors, sepClus };
}
void ?{}( Executor & ex ) {                                                             // special for current cluster, no processors added
        ex{ 0, active_cluster()->nprocessors, false };
}
void ^?{}( Executor & ex ) with(ex) {
        // Add one sentinel per worker to stop them. Since in destructor, no new external work should be queued.  Cannot
        // combine next two loops and only have a single sentinel because workers arrive in arbitrary order, so worker1 may
        // take the single sentinel while waiting for worker 0 to end.

        WRequest sentinel[nworkers];
        unsigned int reqPerWorker = nrqueues / nworkers;
        for ( unsigned int i = 0, step = 0; i < nworkers; i += 1, step += reqPerWorker ) {
                insert( requests[step], &sentinel[i] );                 // force eventually termination
        } // for
        for ( i; nworkers ) {
                delete( workers[i] );
        } // for
        for ( i; nprocessors ) {
                delete( processors[i] );
        } // for

        free( workers );
//      adelete( nrqueues, requests );
        for ( i; nrqueues ) ^?{}( requests[i] );                        // FIX ME: problem with resolver
        free( requests );
        free( processors );
        if ( sepClus ) { delete( cluster ); }
} // ^?{}

void send( Executor & ex, void (* action)( void ) ) {   // asynchronous call, no return value
        WRequest * node = new( action );
        insert( ex.requests[tickets( ex )], node );
} // send


int counter = 0;

void work( void ) {
        __atomic_add_fetch( &counter, 1, __ATOMIC_SEQ_CST );
        // fprintf( stderr, "workie\n" );
}

int main( int argc, char * argv[] ) {
        int times = 1_000_000;
        if ( argc == 2 ) times = atoi( argv[1] );
        processor p[7];
        {
                Executor exector;
                for ( i; times ) {
                        send( exector, work );
                        if ( i % 100 == 0 ) yield();
                } // for
        }
        printf( "%d\n", counter );
}

// Local Variables: //
// tab-width: 4" //
// compile-command: "cfa executor.cfa" //
// End: //