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127 lines
4.0 KiB
127 lines
4.0 KiB
.\"
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.\" Copyright 2012-2013 Samy Al Bahra.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\"
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.Dd April 20, 2013
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.Dt CK_RING_TRYDEQUEUE_SPMC 3
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.Sh NAME
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.Nm ck_ring_trydequeue_spmc
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.Nd dequeue from bounded FIFO and allow for spurious failure
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.Sh LIBRARY
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Concurrency Kit (libck, \-lck)
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.Sh SYNOPSIS
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.In ck_ring.h
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.Ft bool
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.Fn ck_ring_trydequeue_spmc "ck_ring_t *ring" "ck_ring_buffer_t *buffer" "void *result"
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.Sh DESCRIPTION
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The
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.Fn ck_ring_trydequeue_spmc 3
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function attempts to dequeue a pointer from the bounded buffer
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pointed to by
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.Fa ring
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in FIFO fashion. The pointer is stored in the pointer
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pointed to by
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.Fa result .
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The buffer pointed to by
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.Fa buffer
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must be unique to
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.Fa ring
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and point to an array of ck_ring_buffer_t of sufficient
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length (according to the power-of-2 elements in the buffer).
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The decoupling of the ring from the buffer serves
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to address use-cases involving multiple address spaces
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and DMA, among others.
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If you are on non-POSIX platforms or wish for strict
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compliance with C, then it is recommended to pass a
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pointer of type void ** for
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.Fa result .
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This function is safe to call without locking for UINT_MAX
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concurrent
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.Fn ck_ring_dequeue_spmc 3
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or
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.Fn ck_ring_trydequeue_spmc 3
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invocations and up to one concurrent
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.Fn ck_ring_enqueue_spmc 3
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or
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.Fn ck_ring_tryenqueue_spmc 3
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invocation. This operation will always complete
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in a bounded number of steps. It is
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possible for the function to return false even
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if
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.Fa ring
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is non-empty. This
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.Sh EXAMPLE
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.Bd -literal -offset indent
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#include <ck_ring.h>
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/* This ring was previously initialized with ck_ring_init. */
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ck_ring_t ring;
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/* The ring was initialized for 1023 elements. */
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ck_ring_buffer_t buffer[1024];
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void
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dequeue(void)
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{
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void *result;
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/* Dequeue from ring until contention is actively observed. */
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while (ck_ring_trydequeue_spmc(&ring, &buffer, &result) == true) {
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/*
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* Results contains the oldest pointer in ring
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* since the dequeue operation returned true.
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*/
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operation(result);
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}
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/* An empty ring was encountered, leave. */
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return;
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}
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.Ed
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.Sh RETURN VALUES
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The function returns true if the dequeue operation
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completely successfully in a bounded number of steps.
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The result of the dequeue operation is stored in the
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value pointed to by
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.Fa result .
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Otherwise, the function will return false if the buffer was empty
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or if the operation could not be completed in a bounded
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number of steps. If the function returns false, then the contents
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of
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.Fa result
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are undefined.
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.Sh SEE ALSO
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.Xr ck_ring_init 3 ,
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.Xr ck_ring_dequeue_spmc 3 ,
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.Xr ck_ring_enqueue_spmc 3 ,
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.Xr ck_ring_enqueue_spmc_size 3 ,
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.Xr ck_ring_dequeue_spsc 3 ,
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.Xr ck_ring_enqueue_spsc 3 ,
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.Xr ck_ring_enqueue_spsc_size 3 ,
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.Xr ck_ring_capacity 3 ,
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.Xr ck_ring_size 3
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.Pp
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Additional information available at http://concurrencykit.org/
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