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+PR_OpenSharedMemory
+===================
+
+Opens an existing shared memory segment or, if one with the specified
+name doesn't exist, creates a new one.
+
+
+Syntax
+------
+
+.. code::
+
+   #include <prshm.h>
+
+   NSPR_API( PRSharedMemory * )
+     PR_OpenSharedMemory(
+        const char             *name,
+        PRSize             size,
+        PRIntn             flags,
+        PRIntn             mode
+   );
+
+   /* Define values for PR_OpenShareMemory(...,create) */
+   #define PR_SHM_CREATE 0x1  /* create if not exist */
+   #define PR_SHM_EXCL   0x2  /* fail if already exists */
+
+
+Parameters
+~~~~~~~~~~
+
+The function has the following parameters:
+
+name
+   The name of the shared memory segment.
+size
+   The size of the shared memory segment.
+flags
+   Options for creating the shared memory.
+mode
+   Same as passed to :ref:`PR_Open`.
+
+
+Returns
+~~~~~~~
+
+Pointer to opaque structure ``PRSharedMemory``, or ``NULL`` if an error
+occurs. Retrieve the reason for the failure by calling :ref:`PR_GetError`
+and :ref:`PR_GetOSError`.
+
+
+Description
+-----------
+
+:ref:`PR_OpenSharedMemory` creates a new shared memory segment or
+associates a previously created memory segment with the specified name.
+When parameter ``create`` is (``PR_SHM_EXCL`` \| ``PR_SHM_CREATE``) and
+the shared memory already exists, the function returns ``NULL`` with the
+error set to ``PR_FILE_EXISTS_ERROR``.
+
+When parameter ``create`` is ``PR_SHM_CREATE`` and the shared memory
+already exists, a handle to that memory segment is returned. If the
+segment does not exist, it is created and a pointer to the related
+``PRSharedMemory`` structure is returned.
+
+When parameter ``create`` is 0, and the shared memory exists, a pointer
+to a ``PRSharedMemory`` structure is returned. If the shared memory does
+not exist, ``NULL`` is returned with the error set to
+``PR_FILE_NOT_FOUND_ERROR``.