NAME

       Coro::Semaphore - counting semaphores

SYNOPSIS

        use Coro;

        $sig = new Coro::Semaphore [initial value];

        $sig->down; # wait for signal

        # ... some other "thread"

        $sig->up;

DESCRIPTION

       This module implements counting semaphores. You can initialize a mutex with any level of parallel users,
       that is, you can intialize a sempahore that can be "down"ed more than once until it blocks. There is no
       owner associated with semaphores, so one thread can "down" it while another can "up" it (or vice versa),
       "up" can be called before "down" and so on: the semaphore is really just an integer counter that
       optionally blocks when it is 0.

       Counting semaphores are typically used to coordinate access to resources, with the semaphore count
       initialized to the number of free resources. Threads then increment the count when resources are added
       and decrement the count when resources are removed.

       You don't have to load "Coro::Semaphore" manually, it will be loaded automatically when you "use Coro"
       and call the "new" constructor.

       new [inital count]
           Creates  a new sempahore object with the given initial lock count. The default lock count is 1, which
           means it is unlocked by default. Zero (or negative values)  are  also  allowed,  in  which  case  the
           semaphore is locked by default.

       $sem->count
           Returns the current semaphore count.

       $sem->adjust ($diff)
           Atomically adds the amount given to the current semaphore count. If the count becomes positive, wakes
           up any waiters. Does not block if the count becomes negative, however.

       $sem->down
           Decrement  the  counter,  therefore "locking" the semaphore. This method waits until the semaphore is
           available if the counter is zero.

       $sem->wait
           Similar to "down", but does not actually decrement the counter. Instead, when this function  returns,
           a  following call to "down" or "try" is guaranteed to succeed without blocking, until the next thread
           switch ("cede" etc.).

           Note that using "wait" is much less efficient than using "down", so try  to  prefer  "down"  whenever
           possible.

       $sem->wait ($callback)
           If  you  pass  a  callback argument to "wait", it will not wait, but immediately return. The callback
           will be called as soon as the semaphore becomes available (which might be instantly), and gets passed
           the semaphore as first argument.

           The callback might "down" the semaphore exactly once, might wake up other threads, but is NOT allowed
           to block (switch to other threads).

       $sem->up
           Unlock the semaphore again.

       $sem->try
           Try to "down" the semaphore. Returns true when this was possible, otherwise return  false  and  leave
           the semaphore unchanged.

       $sem->waiters
           In scalar context, returns the number of threads waiting for this semaphore. Might accidentally cause
           WW3 if called in other contexts, so don't use these.

       $guard = $sem->guard
           This  method  calls  "down"  and  then  creates a guard object. When the guard object is destroyed it
           automatically calls "up".

AUTHOR

        Marc Lehmann <schmorp@schmorp.de>
        http://home.schmorp.de/

perl v5.18.1                                       2013-11-18                                     Semaphore(3pm)