110 lines
5 KiB
HTML
110 lines
5 KiB
HTML
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<title>9p-intmap(3) - Plan 9 from User Space</title>
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<meta content="text/html; charset=utf-8" http-equiv=Content-Type>
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<tr height=10><td>
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<tr><td width=20><td>
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<tr><td width=20><td><b>9P-INTMAP(3)</b><td align=right><b>9P-INTMAP(3)</b>
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<tr><td width=20><td colspan=2>
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<br>
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<p><font size=+1><b>NAME </b></font><br>
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<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
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Intmap, allocmap, freemap, insertkey, caninsertkey, lookupkey,
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deletekey – integer to data structure maps<br>
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</table>
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<p><font size=+1><b>SYNOPSIS </b></font><br>
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<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
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<tt><font size=+1>#include <u.h><br>
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#include <libc.h><br>
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#include <fcall.h><br>
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#include <thread.h><br>
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#include <9p.h><br>
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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Intmap* allocmap(void (*inc)(void*))<br>
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void freemap(Intmap *map, void (*dec)(void*))<br>
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void* lookupkey(Intmap *map, ulong key)<br>
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void* insertkey(Intmap *map, ulong key, void *val)<br>
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int caninsertkey(Intmap *map, ulong key, void *val)<br>
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void* lookupkey(Intmap *map, ulong key)<br>
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void* deletekey(Intmap *map, ulong key)<br>
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</font></tt>
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</table>
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<p><font size=+1><b>DESCRIPTION </b></font><br>
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<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
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An <tt><font size=+1>Intmap</font></tt> is an arbitrary mapping from integers to pointers. <i>Allocmap</i>
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creates a new map, and <i>freemap</i> destroys it. The <i>inc</i> function is
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called each time a new pointer is added to the map; similarly,
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<i>dec</i> is called on each pointer left in the map when it is being
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freed. Typically these functions maintain reference counts.
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New entries are added to the map by calling <i>insertkey</i>, which will
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return the previous value associated with the given <i>key</i>, or zero
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if there was no previous value. <i>Caninsertkey</i> is like <i>insertkey</i>
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but only inserts <i>val</i> if there is no current mapping. It returns
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1 if <i>val</i> was inserted, 0 otherwise. <i>Lookupkey</i> returns the pointer
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associated with <i>key</i>, or zero if there is no such pointer. <i>Deletekey</i>
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removes the entry for <i>id</i> from the map, returning the associated
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pointer, if any.
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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Concurrent access to <tt><font size=+1>Intmap</font></tt>s is safe, moderated via a <tt><font size=+1>QLock</font></tt> stored
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in the <tt><font size=+1>Intmap</font></tt> structure.
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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In anticipation of the storage of reference-counted structures,
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an increment function <i>inc</i> may be specified at map creation time.
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<i>Lookupkey</i> calls <i>inc</i> (if non-zero) on pointers before returning
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them. If the reference count adjustments were left to the caller
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(and thus not protected by the lock), it would be possible to
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accidentally reclaim a structure if, for example, it was deleted
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from the map and its reference count decremented between the return
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of <i>insertkey</i> and the external increment. <i>Insertkey</i> and <i>caninsertkey</i>
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do <i>not</i> call <i>inc</i> when inserting <i>val</i> into the map, nor do <i>insertkey</i>
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or <i>deletekey</i> call <i>inc</i> when returning old map entries.
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The rationale is that calling an insertion function transfers
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responsibility for the reference to the map, and responsibility
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is given back via the return value of <i>deletekey</i> or the next <i>insertkey</i>.
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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<tt><font size=+1>Intmap</font></tt>s are used by the 9P library to implement <tt><font size=+1>Fidpool</font></tt>s and <tt><font size=+1>Reqpool</font></tt>s.<br>
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</table>
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<p><font size=+1><b>SOURCE </b></font><br>
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<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
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<tt><font size=+1>/usr/local/plan9/src/lib9p/intmap.c<br>
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</font></tt>
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</table>
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<p><font size=+1><b>SEE ALSO </b></font><br>
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<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
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<a href="../man3/9p.html"><i>9p</i>(3)</a>, <a href="../man3/9p-fid.html"><i>9p-fid</i>(3)</a><br>
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</table>
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<td width=20>
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<tr height=20><td>
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</table>
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