source: doc/papers/concurrency/examples/RWMonitorEXT.cfa @ 2210cfc

#include <fstream.hfa>
#include <thread.hfa>

volatile int SharedRW = 0;                                                              // shared variable to test readers and writers

monitor ReadersWriter {
        int rcnt, wcnt;                                                                         // number of readers/writer using resource
};

void ?{}( ReadersWriter & rw ) with(rw) { rcnt = wcnt = 0; }
void EndRead( ReadersWriter & mutex rw ) with(rw) { rcnt -= 1; }
void EndWrite( ReadersWriter & mutex rw ) with(rw) { wcnt = 0; }
void StartRead( ReadersWriter & mutex rw ) with(rw) {
        if ( wcnt > 0 ) waitfor( EndWrite : rw );
        rcnt += 1;
}
void StartWrite( ReadersWriter & mutex rw ) with(rw) {
        if ( wcnt > 0 ) waitfor( EndWrite : rw );
        else while ( rcnt > 0 ) waitfor( EndRead : rw );
        wcnt = 1;
}
int readers( ReadersWriter & rw ) { return rw.rcnt; }

void Read( ReadersWriter & rw ) {
        StartRead( rw );
        sout | "Reader:" | active_thread() | ", shared:" | SharedRW | " with:" | readers( rw ) | " readers";
        yield( 3 );
        EndRead( rw );
}
void Write( ReadersWriter & rw ) {
        StartWrite( rw );

        SharedRW += 1;
        sout | "Writer:" | active_thread() | ",  wrote:" | SharedRW;
        yield( 1 );
        EndWrite( rw );
}

thread Worker {
        ReadersWriter &rw;
};
void ?{}( Worker & w, ReadersWriter * rw ) { &w.rw = rw; }
void main( Worker & w ) with(w) {
        for ( 10 ) {
                if ( rand() % 100 < 70 ) {                                      // decide to be a reader or writer
                        Read( rw );
                } else {
                        Write( rw );
                } // if
        } // for
}

int main() {
        enum { MaxTask = 5 };
        ReadersWriter rw;
        Worker *workers[MaxTask];

        for ( i; MaxTask ) workers[i] = new( &rw );
        for ( i; MaxTask ) delete( workers[i] );
        sout | "successful completion";
} // main

// Local Variables: //
// tab-width: 4 //
// compile-command: "cfa -O2 RWMonitorEXT.cfa" //
// End: //