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<! "@(#)get.so 10.8 (Sleepycat) 9/29/98">
<!Copyright 1997, 1998 by Sleepycat Software, Inc. All rights reserved.>
<html>
<body bgcolor=white>
<head>
<title>Berkeley DB: DbMpoolFile::get</title>
<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
<meta name="keywords" content="embedded,database,programmatic,toolkit,b+tree,btr
ee,hash,hashing,transaction,transactions,locking,logging,access method,access me
thods,java,C,C++">
</head>
<h1>DbMpoolFile::get</h1>
<hr size=1 noshade>
<tt>
<h3>
<pre>
#include <db_cxx.h>
<p>
int
DbMpoolFile::get(db_pgno_t *pgnoaddr, u_int32_t flags, void **pagep);
</pre>
</h3>
<h1>Description</h1>
<p>
The DbMpoolFile::get method copies a pointer to the page with the page
number specified by <b>pgnoaddr</b>, from the source file in the
<a href="../../api_cxx/DbMpoolFile/class.html">DbMpoolFile</a>, into the memory location referenced by <b>pagep</b>.
If the page does not exist or cannot be retrieved, DbMpoolFile::get will
fail.
<p>
<b>Page numbers begin at 0, i.e., the first page in the file is
page number 0, not page number 1.</b>
<p>
The returned page is <b>size_t</b> type aligned.
<p>
The <b>flags</b> argument is specified by logically <b>OR</b>'ing together one or more
of the following values:
<dl compact>
<a name="DB_MPOOL_CREATE">
<p><dt>DB_MPOOL_CREATE<dd>If the specified page does not exist, create it. In this case,
<a href="../DbMpool/db_register.html#pgin">the pgin method</a>,
if specified, is called.
<a name="DB_MPOOL_LAST">
<p><dt>DB_MPOOL_LAST<dd>Return the last page of the source file and copy its page number
to the location referenced by <b>pgnoaddr</b>.
<a name="DB_MPOOL_NEW">
<p><dt>DB_MPOOL_NEW<dd>Create a new page in the file and copy its page number to the location
referenced by <b>pgnoaddr</b>. In this case,
<a href="../DbMpool/db_register.html#pgin">the pgin method</a>,
if specified, is <b>not</b> called.
</dl>
<p>
The DB_MPOOL_CREATE, DB_MPOOL_LAST and DB_MPOOL_NEW flags are mutually
exclusive.
<p>
Created pages have all their bytes set to 0, unless otherwise specified
when the file was opened.
<p>
All pages returned by DbMpoolFile::get will be retained (i.e.
<i>pinned</i> in the pool until a subsequent call to <a href="../../api_cxx/DbMpoolFile/put.html">DbMpoolFile::put</a>.
<p>
The DbMpoolFile::get
method either returns <b>errno</b> or throws an exception that
encapsulates an <b>errno</b> on failure, and 0 on success.
<p>
<h1>Errors</h1>
If a fatal error occurs in Berkeley DB, the DbMpoolFile::get method may fail and either
return DB_RUNRECOVERY or throw an exception encapsulating DB_RUNRECOVERY,
at which point all subsequent database calls will also fail in the same
way. Methods marked as returning <b>errno</b> will, by default, throw
an exception that encapsulates the error information. The default error
behavior can be changed, see <a href="../../api_cxx/DbException/class.html">DbException</a>.
<p>
The DbMpoolFile::get
method may fail and throw an exception
for any of the errors specified for the following Berkeley DB and C library
functions:
DBmemp->pgin(3),
DBmemp->pgout(3),
abort(3),
close(3),
dbenv->db_paniccall(3),
fcntl(3),
fflush(3),
fprintf(3),
free(3),
fstat(3),
fsync(3),
getenv(3),
getpid(3),
getuid(3),
isdigit(3),
<a href="../../api_cxx/DbLog/compare.html">DbLog::compare</a>,
<a href="../../api_cxx/DbLog/flush.html">DbLog::flush</a>,
lseek(3),
malloc(3),
memcmp(3),
memcpy(3),
memset(3),
mmap(3),
open(3),
pread(3),
pstat_getdynamic(3),
pwrite(3),
read(3),
sigfillset(3),
sigprocmask(3),
stat(3),
strerror(3),
strlen(3),
sysconf(3),
time(3),
unlink(3),
vfprintf(3),
vsnprintf(3),
and
write(3).
<p>
In addition, the DbMpoolFile::get
method may fail and throw an exception
or return <b>errno</b>
for the following conditions:
<dl compact>
<p><dt>EAGAIN<dd>The page reference count has overflowed.
(This should never happen unless there's a bug in the application.)
</dl>
<dl compact>
<p><dt>EINVAL<dd>An invalid flag value or parameter was specified.
<p>
The DB_MPOOL_NEW flag was set and the source file was not opened for writing.
<p>
The requested page does not exist and DB_MPOOL_CREATE was not set.
<p>
More than one of DB_MPOOL_CREATE, DB_MPOOL_LAST and DB_MPOOL_NEW was set.
</dl>
<dl compact>
<p><dt>ENOMEM<dd>The cache is full and no more pages will fit in the pool.
</dl>
<p>
<h1>Class</h1>
<a href="../../api_cxx/DbMpoolFile/class.html">DbMpoolFile</a>
<p>
<h1>See Also</h1>
<a href="../../api_cxx/DbMpoolFile/close.html">DbMpoolFile::close</a>,
DbMpoolFile::get,
<a href="../../api_cxx/DbMpoolFile/open.html">DbMpoolFile::open</a>,
<a href="../../api_cxx/DbMpoolFile/put.html">DbMpoolFile::put</a>,
<a href="../../api_cxx/DbMpoolFile/set.html">DbMpoolFile::set</a>
and
<a href="../../api_cxx/DbMpoolFile/sync.html">DbMpoolFile::sync</a>.
</tt>
</body>
</html>
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