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+PR_CEnterMonitor
+================
+
+Enters the lock associated with a cached monitor.
+
+
+Syntax
+------
+
+.. code::
+
+   #include <prcmon.h>
+
+   PRMonitor* PR_CEnterMonitor(void *address);
+
+
+Parameter
+~~~~~~~~~
+
+The function has the following parameter:
+
+``address``
+   A reference to the data that is to be protected by the monitor. This
+   reference must remain valid as long as there are monitoring
+   operations being performed.
+
+
+Returns
+~~~~~~~
+
+The function returns one of the following values:
+
+-  If successful, the function returns a pointer to the :ref:`PRMonitor`
+   associated with the value specified in the ``address`` parameter.
+-  If unsuccessful (the monitor cache needs to be expanded and the
+   system is out of memory), the function returns ``NULL``.
+
+
+Description
+-----------
+
+:ref:`PR_CEnterMonitor` uses the value specified in the ``address``
+parameter to find a monitor in the monitor cache, then enters the lock
+associated with the monitor. If no match is found, an available monitor
+is associated with the address and the monitor's entry count is
+incremented (so it has a value of one). If a match is found, then either
+the calling thread is already in the monitor (and this is a reentrant
+call) or another thread is holding the monitor's mutex. In the former
+case, the entry count is simply incremented and the function returns. In
+the latter case, the calling thread is likely to find the monitor locked
+by another thread and waits for that thread to exit before continuing.
+
+.. note::
+
+   **Note**: :ref:`PR_CEnterMonitor` and :ref:`PR_CExitMonitor` must be
+   paired--that is, there must be an exit for every entry--or the object
+   will never become available for any other thread.