Adding upstream version 0.6.0.upstream/0.6.0

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+.\"
+.\" Copyright 2013 Samy Al Bahra.
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"
+.Dd July 26, 2013.
+.Dt ck_sequence 3
+.Sh NAME
+.Nm ck_sequence_init ,
+.Nm ck_sequence_read_begin ,
+.Nm ck_sequence_read_retry ,
+.Nm ck_sequence_write_begin ,
+.Nm ck_sequence_write_end
+.Nd sequence locks
+.Sh LIBRARY
+Concurrency Kit (libck, \-lck)
+.Sh SYNOPSIS
+.In ck_sequence.h
+.Pp
+.Dv ck_sequence_t seqlock = CK_SEQUENCE_INITIALIZER;
+.Pp
+.Ft void
+.Fn ck_sequence_init "ck_sequence_t *sq"
+.Ft unsigned int
+.Fn ck_sequence_read_begin "const ck_sequence_t *sq"
+.Ft bool
+.Fn ck_sequence_read_retry "const ck_sequence_t *sq" "unsigned int version"
+.Ft void
+.Fn ck_sequence_write_begin "ck_sequence_t *sq"
+.Ft void
+.Fn ck_sequence_write_end "ck_sequence_t *sq"
+.Sh DESCRIPTION
+It is recommended to use ck_sequence when a small amount of data that cannot be
+accessed atomically has to be synchronized with readers in a fashion that does
+not block any writer. Readers are able to execute their read-side critical
+sections without any atomic operations. A ck_sequence_t must be initialized
+before use. It may be initialized using either a static initializer
+(CK_SEQUENCE_INITIALIZER) or using
+.Fn ck_sequence_init .
+Before readers attempt to
+read data that may be concurrently modified they must first save the return
+value of
+.Fn ck_sequence_read_begin .
+While or after a reader has completed copying
+the data associated with a ck_sequence_t it must pass the earlier return value
+of
+.Fn ck_sequence_read_begin
+to
+.Fn "ck_sequence_read_retry". If
+.Fn ck_sequence_read_retry
+returns true then the copy of data may be inconsistent and the read process
+must be retried. Writers must rely on their own synchronization primitives.
+Once a writer has entered its respective critical section, it must call
+.Fn ck_sequence_write_begin
+to signal intent to update the data protected
+by the ck_sequence_t. Before the writer leaves its critical section it must
+execute
+.Fn ck_sequence_write_end
+to indicate that the updates have left respective objects in a consistent state.
+.Sh EXAMPLE
+.Bd -literal -offset indent
+#include <ck_sequence.h>
+#include <stdlib.h>
+
+static struct example {
+	int a;
+	int b;
+	int c;
+} global;
+
+static ck_sequence_t seqlock = CK_SEQUENCE_INITIALIZER;
+
+void
+reader(void)
+{
+	struct example copy;
+	unsigned int version;
+
+	/*
+	 * Attempt a read of the data structure. If the structure
+	 * has been modified between ck_sequence_read_begin and
+	 * ck_sequence_read_retry then attempt another read since
+	 * the data may be in an inconsistent state.
+	 */
+	do {
+		version = ck_sequence_read_begin(&seqlock);
+		copy = global;
+	} while (ck_sequence_read_retry(&seqlock, version));
+
+	/*
+	 * The previous may also be expressed using CK_SEQUENCE_READ.
+	 * Generally recommend to only use ck_sequence_read_retry
+	 * if you would like to detect a conflicting write at some
+	 * higher granularity.
+	 */
+	CK_SEQUENCE_READ(&seqlock, &version) {
+		copy = global;
+	}
+
+	return;
+}
+
+void
+writer(void)
+{
+
+	for (;;) {
+		ck_sequence_write_begin(&seqlock);
+		global.a = rand();
+		global.b = global.a + global.b;
+		global.c = global.b + global.c;
+		ck_sequence_write_end(&seqlock);
+	}
+
+	return;
+}
+.Ed
+.Sh SEE ALSO
+.Xr ck_brlock 3 ,
+.Xr ck_bytelock 3 ,
+.Xr ck_rwlock 3
+.Pp
+Additional information available at http://concurrencykit.org/