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(Arbiters): Tweak wording for clarity, note any

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thread can unlock not just the one which locked.
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Kevin Ryde 2004-08-05 00:38:13 +00:00
parent f070ba1332
commit e136aab0cc
1 changed files with 16 additions and 16 deletions
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32
doc/ref/api-scheduling.texi
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@ -25,36 +25,36 @@ reviewed and largely reorganized.]
@node Arbiters
@subsection Arbiters
@cindex arbiters
@c FIXME::martin: Review me!
Arbiters are synchronization objects, they can be used by threads to
control access to a shared resource. An arbiter can be locked to
indicate a resource is in use, and unlocked when done.
Arbiters are synchronization objects. They are created with
@code{make-arbiter}. Two or more threads can synchronize on an arbiter
by trying to lock it using @code{try-arbiter}. This call will succeed
if no other thread has called @code{try-arbiter} on the arbiter yet,
otherwise it will fail and return @code{#f}. Once an arbiter is
successfully locked, it cannot be locked by another thread until the
thread holding the arbiter calls @code{release-arbiter} to unlock it.
An arbiter is like a light-weight mutex (@pxref{Low level thread
primitives}). It uses less memory and may be a little faster, but
there's no way for a thread to block waiting on an arbiter, it can
only test and get the status returned.
@deffn {Scheme Procedure} make-arbiter name
@deffnx {C Function} scm_make_arbiter (name)
Return an object of type arbiter and name @var{name}. Its
state is initially unlocked. Arbiters are a way to achieve
process synchronization.
Return an arbiter object, initially unlocked. Currently @var{name} is
only used for diagnostic output.
@end deffn
@deffn {Scheme Procedure} try-arbiter arb
@deffnx {C Function} scm_try_arbiter (arb)
Return @code{#t} and lock the arbiter @var{arb} if the arbiter
was unlocked. Otherwise, return @code{#f}.
If @var{arb} is unlocked, then lock it and return @code{#t}. If
@var{arb} is already locked, then do nothing and return @code{#f}.
@end deffn
@deffn {Scheme Procedure} release-arbiter arb
@deffnx {C Function} scm_release_arbiter (arb)
Return @code{#t} and unlock the arbiter @var{arb} if the
arbiter was locked. Otherwise, return @code{#f}.
If @var{arb} is locked, then unlock it and return @code{#t}. If
@var{arb} is already unlocked, then do nothing and return @code{#f}.
Typical usage is for the thread which locked an arbiter to later
release it, but that's not required, any thread can release it.
@end deffn