source: libcfa/src/executor.cfa @ 16a18f3

// 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 <bits/containers.hfa>
#include <thread.hfa>
#include <stdio.h>

forall( otype T | is_node(T) | is_monitor(T) ) {
    monitor Buffer {                                    // unbounded buffer
        __queue_t( T ) queue;                           // unbounded list of work requests
        condition delay;
    }; // Buffer

    void insert( Buffer( T ) & mutex buf, T * elem ) with(buf) {
        append( queue, elem );                          // insert element into buffer
        signal( delay );                                // restart
    } // insert

    T * remove( Buffer( T ) & mutex buf ) with(buf) {
        if ( ! queue ) wait( delay );                   // no request to process ? => wait
        return pop_head( queue );
    } // remove
} // distribution

struct WRequest {                                       // client request, no return
    void (* action)( void );
    WRequest * next;                                    // intrusive queue field
}; // WRequest

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

// Each worker has its own work buffer to reduce contention between client and server. Hence, work requests arrive and
// are distributed into buffers in a roughly round-robin order.

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

void main( Worker & w ) with(w) {
    for ( int i = 0;; i = (i + 1) % range ) {
        WRequest * 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 ) {
    (*get_thread(worker)){ *wc };                       // create on given cluster
    worker.[requests, start, range] = [requests, start, range];
} // ?{}

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, nmailboxes;     // number of mailboxes/workers/processor tasks
    bool sepClus;                                       // use same or separate cluster for executor
}; // Executor

static thread_local unsigned int next;                  // demultiplexed across worker buffers
unsigned int tickets( Executor & ex ) with(ex) {
    //return uFetchAdd( next, 1 ) % nmailboxes;
    return next++ % nmailboxes;                         // no locking, interference randomizes
} // tickets

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

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

    unsigned int reqPerWorker = nmailboxes / nworkers, extras = nmailboxes % nworkers;
    for ( unsigned int i = 0, step = 0; i < nworkers; i += 1, step += reqPerWorker + ( i < extras ? 1 : 0 ) ) {
        workers[ i ] = new( cluster, requests, step, reqPerWorker + ( i < extras ? 1 : 0 ) );
    } // 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
    ex{ 0, active_cluster()->nprocessors, false };
}
void ^?{}( Executor & ex ) with(ex) {
    // Add one sentinel per worker to stop them. Since in destructor, no new 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 = nmailboxes / 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

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

int main() {
    {
        Executor exector;
        for ( i; 3000 ) {
            send( exector, workie );
            if ( i % 100 ) yield();
        } // for
    }
    printf( "%d\n", counter );
}

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