64 lines
1.7 KiB
Plaintext
64 lines
1.7 KiB
Plaintext
This library provides two structures to ease concurrent programming:
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* SEMAPHORES
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* WITH-LOCk
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================================================================================
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After installation, use the switch
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-lel concurrency/load.scm
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to load this library.
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================================================================================
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The structure SEMAPHORES defines semaphores to be used this
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threads. Semaphores are usually used to control access to a resource
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by using a counter for the free slots of the resource.
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(make-semaphore init) -> semaphore
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Constructor for semaphores. INIT specifies the initial value of the
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semaphore's counter.
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(semaphore-wait sem) -> unspecific
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Blocks the current thread until at the counter of the semaphore SEM is
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at least one. It then decrements the counter and returns.
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(semaphore-post sem) -> unspecific
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Increments the counter of the semaphore SEM.
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(with-semaphore-posted sem thunk)
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Calls SEMAPHORE-WAIT on SEM before calling THUNK. When THUNK returns,
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calls SEMAPHORE-POST on SEM and returns the return value of THUNK. If
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the evaluation of THUNK causes a non-local exit, SEMAPHORE-POST is
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also applied to SEM, likewise, if the control reenters the dynamic
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extend of the evaluation of THUNK, SEMAPHORE-WAIT is called on SEM.
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The structure WITH-LOCK exports the procedure WITH-LOCK as an
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extension of the lock structure from Scheme 48.
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(with-lock lock thunk)
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This procedure obtains the requested lock, and then calls
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(thunk). When thunk returns, the lock is released. A non-local exit
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(e.g., throwing to a saved continuation or raising an exception) also
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causes the lock to be released.
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After a normal return from thunk, its return values are returned
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by with-lock.
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