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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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| <br> |
| <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> |
| |
| <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> |
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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>. |
| |
| <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> |
| |
| </table> |
| <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> |
| </table> |
| <p><font size=+1><b>SEE ALSO </b></font><br> |
| |
| <table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td> |
| |
| <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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