Import BSDDB 4.7.25 (as of svn r89086)
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Zachary Ware
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docs/api_c/env_set_thread_id.html
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docs/api_c/env_set_thread_id.html
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<!--$Id: env_set_thread_id.html 63573 2008-05-23 21:43:21Z trent.nelson $-->
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<!--Copyright (c) 1997,2008 Oracle. All rights reserved.-->
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<!--See the file LICENSE for redistribution information.-->
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<html>
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<head>
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<title>Berkeley DB: DB_ENV->set_thread_id</title>
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<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
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<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++">
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</head>
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<body bgcolor=white>
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<table width="100%"><tr valign=top>
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<td>
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<b>DB_ENV->set_thread_id</b>
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</td>
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<td align=right>
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<a href="../api_c/api_core.html"><img src="../images/api.gif" alt="API"></a>
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<a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a></td>
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</tr></table>
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<hr size=1 noshade>
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<tt>
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<b><pre>
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#include <db.h>
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<p>
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int
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DB_ENV->set_thread_id(DB_ENV *dbenv,
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void (*thread_id)(DB_ENV *dbenv, pid_t *pid, db_threadid_t *tid));
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</pre></b>
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<hr size=1 noshade>
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<b>Description: DB_ENV->set_thread_id</b>
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<p>Declare a function that returns a unique identifier pair for the current
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thread of control. The DB_ENV->set_thread_id method supports the
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<a href="../api_c/env_failchk.html">DB_ENV->failchk</a> method. For more information, see
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<a href="../ref/cam/app.html">Architecting Data Store and Concurrent
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Data Store applications</a>, and <a href="../ref/transapp/app.html">Architecting Transactional Data Store applications</a>.</p>
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<p>The DB_ENV->set_thread_id method configures operations performed using the specified
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<a href="../api_c/env_class.html">DB_ENV</a> handle, not all operations performed on the underlying
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database environment.</p>
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<p>The DB_ENV->set_thread_id method may be called at any time during the life of the
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application.</p>
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<p>The DB_ENV->set_thread_id method
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returns a non-zero error value on failure
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and 0 on success.
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</p>
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<b>Parameters</b> <br>
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<b>thread_id</b><ul compact><li>The <b>thread_id</b> parameter is a function which returns a unique
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identifier pair for a thread of control in a Berkeley DB application. The
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function takes three arguments:</ul>
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<br>
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<b><b>dbenv</b></b><ul compact><li>The <b>dbenv</b> parameter is the enclosing database environment
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handle, allowing application access to the application-private fields
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of that object.</ul>
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<b><b>pid</b></b><ul compact><li>The <b>pid</b> points to a memory location of type pid_t. The
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process ID of the current thread of control may be returned in
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this memory location.</ul>
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<b><b>tid</b></b><ul compact><li>The <b>tid</b> points to a memory location of type db_threadid_t. The
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thread ID of the current thread of control may be returned in this
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memory location.</ul>
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<br>
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<br>
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<p>The standard system library calls to return process and thread IDs are
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often sufficient for this purpose (for example, getpid() and
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pthread_self() on POSIX systems or GetCurrentThreadID on Windows
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systems). However, if the Berkeley DB application dynamically creates
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processes or threads, some care may be necessary in assigning unique
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IDs. In most threading systems, process and thread IDs are available
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for re-use as soon as the process or thread exits. If a new process or
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thread is created between the time of process or thread exit, and the
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<a href="../api_c/env_failchk.html">DB_ENV->failchk</a> method is run, it may be possible for
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<a href="../api_c/env_failchk.html">DB_ENV->failchk</a> to not detect that a thread of control exited
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without properly releasing all Berkeley DB resources.</p>
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<p>It may be possible to handle this problem by inhibiting process or
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thread creation between thread of control exit and calling
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<a href="../api_c/env_failchk.html">DB_ENV->failchk</a>. Alternatively, the <b>thread_id</b> function
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must be constructed to not re-use <b>pid</b>/<b>tid</b> pairs. For
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example, in a single process application, the returned process ID might
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be used as an incremental counter, with the returned thread ID set to
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the actual thread ID. Obviously, the <b>is_alive</b> function
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specified to the <a href="../api_c/env_set_isalive.html">DB_ENV->set_isalive</a> method must be compatible with any
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<b>thread_id</b> function specified to DB_ENV->set_thread_id.</p>
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<p>The db_threadid_t type is configured to be the same type as a standard
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thread identifier, in Berkeley DB configurations where this type is known (for
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example, systems supporting pthread_t or thread_t, or DWORD on Windows).
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If the Berkeley DB configuration process is unable to determine the type of a
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standard thread identifier, the db_thread_t type is set to uintmax_t (or
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the largest available unsigned integral type, on systems lacking the
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uintmax_t type). Applications running on systems lacking a detectable
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standard thread type, and which are also using thread APIs where a
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thread identifier is not an integral value and so will not fit into the
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configured db_threadid_t type, must either translate between the
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db_threadid_t type and the thread identifier (mapping the thread
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identifier to a unique identifier of the appropriate size), or modify
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the Berkeley DB sources to use an appropriate db_threadid_t type. Note: we
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do not currently know of any systems where this is necessary. If your
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application has to solve this problem, please contact our support group
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and let us know.</p>
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<p>If no <b>thread_id</b> function is specified by the application, the
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Berkeley DB library will identify threads of control by using the taskIdSelf()
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call on VxWorks, the getpid() and GetCurrentThreadID() calls on Windows,
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the getpid() and pthread_self() calls when the Berkeley DB library has been
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configured for POSIX pthreads or Solaris LWP threads, the getpid() and
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thr_self() calls when the Berkeley DB library has been configured for UI
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threads, and otherwise getpid().</p>
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<br><b>Errors</b>
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<p>The DB_ENV->set_thread_id method
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may fail and return one of the following non-zero errors:</p>
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<br>
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<b>EINVAL</b><ul compact><li>An
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invalid flag value or parameter was specified.</ul>
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<br>
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<hr size=1 noshade>
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<br><b>Class</b>
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<a href="../api_c/env_class.html">DB_ENV</a>
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<br><b>See Also</b>
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<a href="../api_c/env_list.html">Database Environments and Related Methods</a>
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</tt>
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<table width="100%"><tr><td><br></td><td align=right>
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<a href="../api_c/api_core.html"><img src="../images/api.gif" alt="API"></a><a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a>
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</td></tr></table>
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<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font>
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</body>
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</html>
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