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