39 lines
1.5 KiB
Factor
39 lines
1.5 KiB
Factor
! Copyright (C) 2008 Slava Pestov.
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! See http://factorcode.org/license.txt for BSD license.
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USING: help.markup help.syntax ;
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IN: concurrency.flags
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HELP: flag
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{ $class-description "A flag allows one thread to notify another when a condition is satisfied." } ;
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HELP: <flag>
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{ $values { "flag" flag } }
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{ $description "Creates a new flag." } ;
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HELP: raise-flag
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{ $values { "flag" flag } }
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{ $description "Raises a flag, notifying any threads waiting on it. Does nothing if the flag has already been raised." } ;
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HELP: wait-for-flag
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{ $values { "flag" flag } }
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{ $description "Waits for a flag to be raised. If the flag has already been raised, returns immediately." } ;
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HELP: lower-flag
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{ $values { "flag" flag } }
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{ $description "Attempts to lower a flag. If the flag has been raised previously, returns immediately, otherwise waits for it to be raised first." } ;
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ARTICLE: "concurrency.flags" "Flags"
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"A " { $emphasis "flag" } " is a condition notification device which can be in one of two states: " { $emphasis "lowered" } " (the initial state) or " { $emphasis "raised" } "."
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$nl
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"The flag can be raised at any time; raising a raised flag does nothing. Lowering a flag if it has not been raised yet will wait for another thread to raise the flag."
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$nl
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"Essentially, a flag can be thought of as a counting semaphore where the count never goes above one."
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{ $subsection flag }
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{ $subsection flag? }
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"Waiting for a flag to be raised:"
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{ $subsection raise-flag }
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{ $subsection wait-for-flag }
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{ $subsection lower-flag } ;
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ABOUT: "concurrency.flags"
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