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47 lines
939 B
Groff
47 lines
939 B
Groff
.\" Copyright (c) 2008-2009 Apple Inc. All rights reserved.
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.Dd May 1, 2009
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.Dt dispatch_once 3
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.Os Darwin
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.Sh NAME
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.Nm dispatch_once
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.Nd execute a block only once
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.Sh SYNOPSIS
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.Fd #include <dispatch/dispatch.h>
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.Ft void
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.Fo dispatch_once
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.Fa "dispatch_once_t *predicate" "void (^block)(void)"
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.Fc
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.Ft void
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.Fo dispatch_once_f
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.Fa "dispatch_once_t *predicate" "void *context" "void (*function)(void *)"
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.Fc
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.Sh DESCRIPTION
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The
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.Fn dispatch_once
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function provides a simple and efficient mechanism to run an initializer
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exactly once, similar to
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.Xr pthread_once 3 .
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Well designed code hides the use of lazy initialization.
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For example:
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.Bd -literal
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FILE *getlogfile(void)
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{
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static dispatch_once_t pred;
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static FILE *logfile;
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dispatch_once(&pred, ^{
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logfile = fopen(MY_LOG_FILE, "a");
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});
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return logfile;
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}
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.Ed
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.Pp
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.Sh FUNDAMENTALS
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The
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.Fn dispatch_once
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function is a wrapper around
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.Fn dispatch_once_f .
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.Sh SEE ALSO
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.Xr dispatch 3
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