The Signal command wakes up one thread that is waiting on the condition variable identified by condId.  The Signal command does not guarantee which thread will be started.

The Signal command does not require the calling thread to hold a lock on the mutex that was used when the waiting threads called Wait.  However, holding the lock while calling Signal allows for a greater level of control over the scheduling of the signaled thread.

If no threads are waiting on the condition variable then nothing happens. Any threads calling Wait after the signal wait as normal.

For more information on using condition variables, see the Condition Variable help page.

Producer := proc( m, cp, cc, max, mindiff )
    global tab, e;
    local i,j,n;

    Threads[Mutex][Lock]( m );
    j := 0;

    tab[ "maxjob" ] := mindiff;
    tab[ "curjob" ] := 1;

    for j from 1 to mindiff
    do
        tab[ j ] := 2*j;
    end do;

    Threads[ConditionVariable][Signal]( cp );

    n := false;
    while ( e )
    do
        j := tab[ "maxjob" ];
        if ( j - tab[ "curjob" ] > mindiff/2 ) then
            n := true;
            Threads[ConditionVariable][Wait]( cp, m );
        end if;

        for i from j to tab[ "curjob" ] + mindiff
        do
            tab[ i ] := 2*i;
        end do;

        tab[ "maxjob" ] := tab[ "curjob" ] + mindiff;

        if ( n ) then
            Threads[ConditionVariable][Broadcast]( cc );
            n := false;
        end if;

    end do;
    Threads[Mutex][Unlock]( m );

end proc:
Consumer := proc( m, cp, cc, max )
    global tab, e;
    local n, i, j, num;

    num := 0;
    Threads[Mutex][Lock]( m );
    while ( num < max )
    do
        while ( tab[ "curjob" ] = tab[ "maxjob" ] )
        do
            Threads[ConditionVariable][Signal]( cp );
            Threads[ConditionVariable][Wait]( cc, m );
        end do;

        n := tab[ "curjob" ];
        j := tab[ n ];
        tab[ "curjob" ] := n + 1;

        Threads[Mutex][Unlock]( m );

        j := add( i, i=1..j );
        num := num+1;

        Threads[Mutex][Lock]( m );
        tab[ n ] := j;
    end do;
    Threads[Mutex][Unlock]( m );
end proc:

$\mathrm{tab}≔\mathrm{table}\left(\right)\&colon;$

$m≔\mathrm{Threads}\left[\mathrm{Mutex}\right]\left[\mathrm{Create}\right]\left(\right)$

$m≔2$

$\mathrm{cc}≔\mathrm{Threads}\left[\mathrm{ConditionVariable}\right]\left[\mathrm{Create}\right]\left(\right)$

$\mathrm{cc}≔1$

$\mathrm{cp}≔\mathrm{Threads}\left[\mathrm{ConditionVariable}\right]\left[\mathrm{Create}\right]\left(\right)$

$\mathrm{cp}≔2$

$e≔\mathrm{true}\&colon;$

$\mathrm{Threads}\left[\mathrm{Mutex}\right]\left[\mathrm{Lock}\right]\left(m\right)$

$\mathrm{id1}≔\mathrm{Threads}\left[\mathrm{Create}\right]\left(\mathrm{Producer}\left(m\&comma;\mathrm{cp}\&comma;\mathrm{cc}\&comma;31\&comma;10\right)\right)$

$\mathrm{id1}≔1$

$\mathrm{Threads}\left[\mathrm{ConditionVariable}\right]\left[\mathrm{Wait}\right]\left(\mathrm{cp}\&comma;m\right)$

$\mathrm{Threads}\left[\mathrm{Mutex}\right]\left[\mathrm{Unlock}\right]\left(m\right)$

$\mathrm{id2}≔\left[\mathrm{seq}\left(\mathrm{Threads}\left[\mathrm{Create}\right]\left(\mathrm{Consumer}\left(m\&comma;\mathrm{cp}\&comma;\mathrm{cc}\&comma;100\right)\right)\&comma;i=1..5\right)\right]$

$\mathrm{id2}≔\left[2\&comma;3\&comma;4\&comma;5\&comma;6\right]$

$\mathrm{Threads}\left[\mathrm{Wait}\right]\left(\mathrm{op}\left(\mathrm{id2}\right)\right)$

$\mathrm{Threads}\left[\mathrm{Mutex}\right]\left[\mathrm{Lock}\right]\left(m\right)$

$e≔\mathrm{false}\&colon;$

$\mathrm{Threads}\left[\mathrm{ConditionVariable}\right]\left[\mathrm{Signal}\right]\left(\mathrm{cp}\right)$

$\mathrm{Threads}\left[\mathrm{Mutex}\right]\left[\mathrm{Unlock}\right]\left(m\right)$

$\mathrm{Threads}\left[\mathrm{Wait}\right]\left(\mathrm{id1}\right)$

$\mathrm{print}\left(\mathrm{tab}\left[''curjob''\right]\right)$

$501$

$\mathrm{print}\left(\mathrm{tab}\left[233\right]\right)$

$108811$

$\mathrm{print}\left(\mathrm{add}\left(i\&comma;i=1..2\cdot 233\right)\right)$

$108811$