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<! "@(#)open.so 10.13 (Sleepycat) 10/4/98">
<!Copyright 1997, 1998 by Sleepycat Software, Inc. All rights reserved.>
<html>
<body bgcolor=white>
<head>
<title>Berkeley DB: DbLockTab::open</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>DbLockTab::open</h1>
<hr size=1 noshade>
<tt>
<h3>
<pre>
#include <db_cxx.h>
<p>
static int
DbLockTab::open(const char *dir,
u_int32_t flags, int mode, DbEnv *dbenv, DbLockTab **regionp);
</pre>
</h3>
<h1>Description</h1>
The DbLockTab::open
method copies a pointer, to the "lock region" identified by the <i>directory</i>
<b>dir</b>, into the memory location referenced by <b>regionp</b>.
<p>
The
<b>dir</b> pathname argument is interpreted as described in
<a href="../../ref/env/naming.html">Berkeley DB File Naming</a>.
<p>
The <b>flags</b> and <b>mode</b> arguments specify how files will be opened
and/or created if they do not already exist.
The flags value is specified by logically <b>OR</b>'ing together one or more of the
following values:
<dl compact>
<a name="DB_CREATE">
<p><dt>DB_CREATE<dd>Create any underlying files, as necessary. If the files do not already
exist and the DB_CREATE flag is not specified, the call will fail.
<a name="DB_THREAD">
<p><dt>DB_THREAD<dd>Cause the m4_reg(DbLockTab) handle returned by DbLockTab::open to be useable
by multiple threads within a single address space, i.e., to be
<i>free-threaded</i>.
</dl>
<p>
All files created by the lock subsystem are created with mode <b>mode</b> (as described
in <b>chmod</b>(2)) and modified by the process' umask value at the time
of creation (see <b>umask</b>(2)))).
The group ownership of created files is based on the system and directory
defaults, and is not further specified by Berkeley DB.
<p>
The locking subsystem is configured
based on the <b>dbenv</b> argument. It is expected that applications
will use a single <a href="../../api_cxx/DbEnv/class.html">DbEnv</a> object as the argument to all of the
subsystems in the Berkeley DB package. The fields of the <a href="../../api_cxx/DbEnv/class.html">DbEnv</a> object
used by DbLockTab::open are described below.
References to the <a href="../../api_cxx/DbEnv/class.html">DbEnv</a> object are maintained by Berkeley DB, so it
is necessary that the object and memory it references be valid until
the object is destroyed.
Any of the <a href="../../api_cxx/DbEnv/class.html">DbEnv</a> fields that are not explicitly set will default
to appropriate values.
<p>
The following fields in the <a href="../../api_cxx/DbEnv/class.html">DbEnv</a> object may be initialized, using
the appropriate set method, before calling DbLockTab::open:
<p>
<dl compact>
<p><dt>void *(*db_errcall)(char *db_errpfx, char *buffer);<dd>
<dt>FILE *db_errfile;<dd>
<dt>const char *db_errpfx;<dd>
<dt>class ostream *db_error_stream;<dd>
<dt>int db_verbose;<dd>The error fields of the <a href="../../api_cxx/DbEnv/class.html">DbEnv</a> behave as described for
<a href="../../api_cxx/DbEnv/appinit.html">DbEnv::appinit</a>.
<a name="lk_conflicts">
<p><dt>const u_int8_t lk_conflicts[][];<dd>A <b>lk_modes</b> by <b>lk_modes</b> array.
A non-0 value for the array element:
<p><ul><pre>lk_conflicts[requested_mode][held_mode]</pre></ul><p>
indicates that requested_mode and held_mode conflict.
The <i>not-granted</i> mode must be represented by 0.
If <b>lk_conflicts</b> is NULL, the conflicts array
<b>db_rw_conflicts</b> is used; see <a href="../../ref/lock/stdmode.html">Standard Lock Modes</a> for a description of that array.
<a name="lk_detect">
<p><dt>db_detect_t lk_detect;<dd>If non-0, specifies that the deadlock detector be run whenever a lock
conflict occurs, and specifies which transaction should be aborted in
the case of a deadlock.
The <b>lk_detect</b> field must be set to one of the following values.
<dl compact>
<a name="DB_LOCK_DEFAULT">
<p><dt>DB_LOCK_DEFAULT<dd>Use the default policy as specified by <a href="../../utility/db_deadlock.html">db_deadlock</a>.
<a name="DB_LOCK_OLDEST">
<p><dt>DB_LOCK_OLDEST<dd>Abort the oldest transaction.
<a name="DB_LOCK_RANDOM">
<p><dt>DB_LOCK_RANDOM<dd>Abort a random transaction involved in the deadlock.
<a name="DB_LOCK_YOUNGEST">
<p><dt>DB_LOCK_YOUNGEST<dd>Abort the youngest transaction.
</dl>
<a name="lk_max">
<p><dt>u_int32_t lk_max;<dd>The maximum number of locks to be held or requested in the table.
This value is used by DbLockTab::open to estimate how much space to
allocate for various lock-table data structures.
If <b>lk_max</b> is 0, a default value is used.
<a name="lk_modes">
<p><dt>u_int32_t lk_modes;<dd>The number of lock modes to be recognized by the lock table (including
the <i>not-granted</i> mode). If <b>lk_modes</b> is 0, the value
<a href="../../ref/lock/stdmode.html">DB_LOCK_RW_N</a> is used.
</dl>
<p>
The DbLockTab::open
method either returns <b>errno</b> or throws an exception that
encapsulates an <b>errno</b> on failure, and 0 on success.
<p>
<h1>Environment Variables</h1>
<dl compact>
<p><dt>DB_HOME<dd>If the <b>dbenv</b> argument to DbLockTab::open was initialized using
<a href="../../api_cxx/DbEnv/appinit.html">DbEnv::appinit</a> the environment variable <b>DB_HOME</b> may
be used as the path of the database home for the interpretation of
the <b>dir</b> argument.
</dl>
<p>
<dl compact>
<p><dt>TMPDIR<dd>If the <b>dbenv</b> argument to DbLockTab::open was NULL or not initialized
using <a href="../../api_cxx/DbEnv/appinit.html">DbEnv::appinit</a> the environment variable <b>TMPDIR</b> may
be used as the directory in which to create the lock table, as described in
DbLockTab::open.
</dl>
<p>
<h1>Errors</h1>
If a fatal error occurs in Berkeley DB, the DbLockTab::open 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 DbLockTab::open
method may fail and throw an exception
for any of the errors specified for the following Berkeley DB and C library
functions:
abort(3),
close(3),
<a href="../../api_cxx/DbEnv/version.html">DbEnv::version</a>,
fcntl(3),
fflush(3),
fprintf(3),
free(3),
fstat(3),
fsync(3),
getenv(3),
getpid(3),
getuid(3),
isdigit(3),
<a href="../../api_cxx/DbLockTab/unlink.html">DbLockTab::unlink</a>,
lseek(3),
malloc(3),
memcpy(3),
memset(3),
mmap(3),
munmap(3),
open(3),
pstat_getdynamic(3),
read(3),
shmat(3),
shmctl(3),
shmdt(3),
sigfillset(3),
sigprocmask(3),
stat(3),
strerror(3),
strlen(3),
sysconf(3),
unlink(3),
vfprintf(3),
vsnprintf(3),
and
write(3).
<p>
In addition, the DbLockTab::open
method may fail and throw an exception
or return <b>errno</b>
for the following conditions:
<dl compact>
<p><dt>EAGAIN<dd>The shared memory region was locked and (repeatedly) unavailable.
</dl>
<dl compact>
<p><dt>EINVAL<dd>An invalid flag value or parameter was specified.
<p>
The DB_THREAD flag was specified and spinlocks are not implemented for
this architecture.
</dl>
<p>
<h1>Class</h1>
<a href="../../api_cxx/DbLockTab/class.html">DbLockTab</a>
<p>
<h1>See Also</h1>
<a href="../../api_cxx/DbLockTab/close.html">DbLockTab::close</a>,
<a href="../../api_cxx/DbLockTab/detect.html">DbLockTab::detect</a>,
<a href="../../api_cxx/DbLockTab/get.html">DbLockTab::get</a>,
<a href="../../api_cxx/DbLockTab/id.html">DbLockTab::id</a>,
DbLockTab::open,
<a href="../../api_cxx/DbLockTab/stat.html">DbLockTab::stat</a>
<a href="../../api_cxx/DbLockTab/unlink.html">DbLockTab::unlink</a>
and
<a href="../../api_cxx/DbLockTab/vec.html">DbLockTab::vec</a>.
</tt>
</body>
</html>
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