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<title>Berkeley DB: DbEnv::mutex_alloc</title>
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DbEnv::mutex_alloc
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#include &lt;db_cxx.h&gt;

int
DbEnv::mutex_alloc(u_int32_t flags, db_mutex_t *mutexp);
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Description: DbEnv::mutex_alloc
The DbEnv::mutex_alloc method allocates a mutex and returns a reference to
it into the memory specified by mutexp.
The DbEnv::mutex_alloc method may not be called before the <a href="../../db4-devel-4.7.25/api_cxx/env_open.html">DbEnv::open</a> method is called.
The DbEnv::mutex_alloc method
either returns a non-zero error value
or throws an exception that encapsulates a non-zero error value on
failure, and returns 0 on success.

Parameters 
 flags<ul compact><li>The flags parameter must be set to 0 or
the following value:
 
<a name="DB_MUTEX_PROCESS_ONLY">DB_MUTEX_PROCESS_ONLY</a><ul compact><li>The mutex is associated with a single process. The <a href="../../db4-devel-4.7.25/api_cxx/env_failchk.html">DbEnv::failchk</a> method
will release mutexes held by any process which has exited.</ul>
<a name="DB_MUTEX_SELF_BLOCK">DB_MUTEX_SELF_BLOCK</a><ul compact><li>The mutex must be self-blocking. That is, if a thread of control locks
the mutex and then attempts to lock the mutex again, the thread of
control will block until another thread of control releases the original
lock on the mutex, allowing the original thread of control to lock the
mutex the second time. Attempting to re-acquire a mutex for which the
DB_MUTEX_SELF_BLOCK flag was not specified will result in
undefined behavior.</ul>
 </ul>
 mutexp<ul compact><li>The mutexp parameter references memory into which
 the mutex reference is copied.</ul> 
 
 Errors
The DbEnv::mutex_alloc method
may fail and throw
<a href="../../db4-devel-4.7.25/api_cxx/except_class.html">DbException</a>,
encapsulating one of the following non-zero errors, or return one of
the following non-zero errors:
 
EINVAL<ul compact><li>An
invalid flag value or parameter was specified.</ul>
 
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 Class
<a href="../../db4-devel-4.7.25/api_cxx/env_class.html">DbEnv</a>
 See Also
<a href="../../db4-devel-4.7.25/api_cxx/env_list.html">Database Environments and Related Methods</a>
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