96 lines
3.4 KiB
Racket
96 lines
3.4 KiB
Racket
#lang scribble/doc
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@require["mz.ss"]
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@title[#:tag "threadcells"]{Thread Cells}
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@declare-exporting[(lib "scheme/thread-cell")]
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A @deftech{thread cell} contains a thread-specific value; that is, it
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contains a specific value for each thread, but it may contain
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different values for different threads. A thread cell is created with
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a default value that is used for all existing threads. When the cell's
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content is changed with @scheme[thread-cell-set!], the cell's value
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changes only for the current thread. Similarly,
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@scheme[thread-cell-ref] obtains the value of the cell that is
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specific to the current thread.
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A thread cell's value can be @deftech{preserved}, which means that
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when a new thread is created, the cell's initial value for the new
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thread is the same as the creating thread's current value. If a thread
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cell is non-preserved, then the cell's initial value for a newly
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created thread is the default value (which was supplied when the cell
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was created).
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Within the current thread, the current values of all preserved threads
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cells can be captured through
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@scheme[current-preserved-thread-cell-values]. The captured set of
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values can be imperatively installed into the current thread through
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another call to @scheme[current-preserved-thread-cell-values]. The
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capturing and restoring threads can be different.
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@defproc[(make-thread-cell [v any/c][preserved? any/c #f]) thread-cell?]{
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Creates and returns a new thread cell. Initially, @scheme[v] is the
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cell's value for all threads. If @scheme[preserved?] is true, then the
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cell's initial value for a newly created threads is the creating
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thread's value for the cell, otherwise the cell's value is initially
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@scheme[v] in all future threads.}
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@defproc[(thread-cell? [v any/c]) boolean?]{
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Returns @scheme[#t] if @scheme[v] is a thread cell created by
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@scheme[make-thread-cell], @scheme[#f] otherwise.}
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@defproc[(thread-cell-ref [cell thread-cell?]) any]{Returns the
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current value of @scheme[cell] for the current thread.}
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@defproc[(thread-cell-set! [cell thread-cell?][v any/c]) any]{Sets the
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value in @scheme[cell] to @scheme[v] for the current thread.}
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@examples[
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(define cnp (make-thread-cell '(nerve) #f))
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(define cp (make-thread-cell '(cancer) #t))
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(thread-cell-ref cnp)
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(thread-cell-ref cp)
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(thread-cell-set! cnp '(nerve nerve))
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(thread-cell-set! cp '(cancer cancer))
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(thread-cell-ref cnp)
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(thread-cell-ref cp)
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(define ch (make-channel))
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(thread (lambda ()
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(channel-put ch (thread-cell-ref cnp))
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(channel-put ch (thread-cell-ref cp))
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(channel-get ch) ; to wait
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(channel-put ch (thread-cell-ref cp))))
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(channel-get ch)
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(channel-get ch)
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(thread-cell-set! cp '(cancer cancer cancer))
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(thread-cell-ref cp)
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(channel-put ch 'ok)
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(channel-get ch)
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]
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@defproc*[([(current-preserved-thread-cell-values) any]
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[(current-preserved-thread-cell-values [thread-cell-vals any/c]) void?])]{
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When called with no arguments, this procedure produces a
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@scheme[thread-cell-vals] that represents the current values (in the
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current thread) for all preserved thread cells.
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When called with a @scheme[thread-cell-vals] generated by a previous
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call to @scheme[current-preserved-thread-cell-values], the values of
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all preserved thread cells (in the current thread) are set to the
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values captured in @scheme[thread-cell-vals]; if a preserved thread
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cell was created after @scheme[thread-cell-vals] was generated, then
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the thread cell's value for the current thread reverts to its initial
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value.}
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