1Semaphore(3) User Contributed Perl Documentation Semaphore(3)
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6 Coro::Semaphore - counting semaphores
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9 use Coro;
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11 $sig = new Coro::Semaphore [initial value];
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13 $sig->down; # wait for signal
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15 # ... some other "thread"
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17 $sig->up;
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20 This module implements counting semaphores. You can initialize a mutex
21 with any level of parallel users, that is, you can initialize a
22 sempahore that can be "down"ed more than once until it blocks. There is
23 no owner associated with semaphores, so one thread can "down" it while
24 another can "up" it (or vice versa), "up" can be called before "down"
25 and so on: the semaphore is really just an integer counter that
26 optionally blocks when it is 0.
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28 Counting semaphores are typically used to coordinate access to
29 resources, with the semaphore count initialized to the number of free
30 resources. Threads then increment the count when resources are added
31 and decrement the count when resources are removed.
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33 You don't have to load "Coro::Semaphore" manually, it will be loaded
34 automatically when you "use Coro" and call the "new" constructor.
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36 new [initial count]
37 Creates a new sempahore object with the given initial lock count.
38 The default lock count is 1, which means it is unlocked by default.
39 Zero (or negative values) are also allowed, in which case the
40 semaphore is locked by default.
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42 $sem->count
43 Returns the current semaphore count. The semaphore can be down'ed
44 without blocking when the count is strictly higher than 0.
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46 $sem->adjust ($diff)
47 Atomically adds the amount given to the current semaphore count. If
48 the count becomes positive, wakes up any waiters. Does not block if
49 the count becomes negative, however.
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51 $sem->down
52 Decrement the counter, therefore "locking" the semaphore. This
53 method waits until the semaphore is available if the counter is
54 zero or less.
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56 $sem->wait
57 Similar to "down", but does not actually decrement the counter.
58 Instead, when this function returns, a following call to "down" or
59 "try" is guaranteed to succeed without blocking, until the next
60 thread switch ("cede" etc.).
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62 Note that using "wait" is much less efficient than using "down", so
63 try to prefer "down" whenever possible.
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65 $sem->wait ($callback)
66 If you pass a callback argument to "wait", it will not wait, but
67 immediately return. The callback will be called as soon as the
68 semaphore becomes available (which might be instantly), and gets
69 passed the semaphore as first argument.
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71 The callback might "down" the semaphore exactly once, might wake up
72 other threads, but is NOT allowed to block (switch to other
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75 $sem->up
76 Unlock the semaphore again.
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78 $sem->try
79 Try to "down" the semaphore. Returns true when this was possible,
80 otherwise return false and leave the semaphore unchanged.
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82 $sem->waiters
83 In scalar context, returns the number of threads waiting for this
84 semaphore. Might accidentally cause WW3 if called in other
85 contexts, so don't use these.
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87 $guard = $sem->guard
88 This method calls "down" and then creates a guard object. When the
89 guard object is destroyed it automatically calls "up".
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92 Marc A. Lehmann <schmorp@schmorp.de>
93 http://software.schmorp.de/pkg/Coro.html
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97perl v5.36.0 2023-01-20 Semaphore(3)