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<concept id="GUID-975F53E5-1C13-5063-B817-795F2623737B" xml:lang="en"><title>Sharable
sessions</title><shortdesc>Describes how a session can be shared by threads.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>A session can be shared by threads provided the server is marked as supporting
shared sessions. </p>
<section id="GUID-33D699D4-50DD-4B46-BFEA-8E9AD46C66C1"><title>Sharing</title> <p>Once a server has started, and a client
has connected to that server (by creating a session), then the client thread
can make the session sharable. There are two types of sharing: </p> <ul>
<li id="GUID-4AF39204-BA70-50CB-9D13-185655322A1D"><p>where the session is
sharable among all threads belonging to the same process as the originating
thread. </p> </li>
<li id="GUID-69DFB418-D434-58B0-A27E-57C053C822A5"><p>where the session is
sharable among all threads in the system, i.e. across all processes. </p> </li>
</ul> <p>A server must support the creation of sharable sessions, otherwise
an attempt to make a session sharable panics the calling thread. Servers can
be created to be either unsharable, sharable among threads in the same process,
or sharable among all threads in the system. </p> <p><b>Sharing
a session among threads in a single process</b> </p> <p>There are two ways
of doing this: </p> <ul>
<li id="GUID-285E2AE9-DEB7-502E-B8B2-47D3B45F50EB"><p>if the session has already
been created, then call <xref href="GUID-6D8A458C-9A39-3000-A3BC-060A2A3663E6.dita#GUID-6D8A458C-9A39-3000-A3BC-060A2A3663E6/GUID-0A453CA9-9DF7-35B8-963E-D75763626136"><apiname>RSessionBase::ShareAuto()</apiname></xref>, which
has the effect of mutating the handle from a thread relative handle to a process
relative handle. The handle can then be shared by the threads. Until this
function is called, the session is specific to the originating thread, and
cannot be used by any other thread. </p> </li>
<li id="GUID-BD414669-EE7A-5821-A591-12D77CD0FBA9"><p>if the session has not
yet been created, then create the session as sharable from the beginning using
one of the overloads of <codeph>RSessionBase::CreateSession()</codeph> that
takes a <codeph>TIpcSessionType</codeph> argument - <i>this is the preferred
method</i>  </p> </li>
</ul> <b>Sharing
a session among threads across all processes</b><p> There are two ways of
doing this:<ul>
<li><p>if the session has already been created, then call <xref href="GUID-6D8A458C-9A39-3000-A3BC-060A2A3663E6.dita#GUID-6D8A458C-9A39-3000-A3BC-060A2A3663E6/GUID-943BCB86-1497-3940-BDA5-6DB1767DA395"><apiname>RSessionBase::ShareProtected()</apiname></xref>,
which has the effect of mutating the handle from a thread relative handle
to a process relative handle; this is also protected and can be passed to
another process. The handle can then be shared by the threads. Until this
function is called, the session is specific to the originating thread, and
cannot be used by any other thread.</p></li>
<li><p>if the session has not yet been created, then create the session as
sharable from the beginning using one of the overloads of <codeph>RSessionBase::CreateSession()</codeph> that
takes a <codeph>TIpcSessionType</codeph> argument - <i>this is the preferred
method</i></p></li>
</ul></p> </section>
<section id="GUID-49F7BFC0-2DD3-4AA5-A105-18ACFE702789"><title>Server exit</title> <p>If the server terminates, all outstanding
messages which have been sent to it are completed with a <codeph>KErrServerTerminated</codeph> code.
Any attempt to send further messages, or to share session, fail immediately
with <codeph>KErrServerTerminated</codeph>. The only valid operation on such
a session is to close it. </p> </section>
<section id="GUID-20F18655-D04E-40CE-8199-058DA9AD1585"><title>Session closure</title> <p>If <codeph>Close()</codeph> is
called on a session, any outstanding messages on the session may not be completed
for the client. Following this, the only message that the server receives
from the session is the disconnect message. </p> </section>
<section id="GUID-C4508E0A-50FC-4780-AEAA-08018CF2AB7F"><title>Client thread exit</title> <p>If a session has not been shared,
then the session is closed as part of normal thread cleanup. </p> <p>If a
session has been shared, the session handle is owned by the process and is
not automatically cleaned up with the thread. In addition, the server is not
informed that the thread has terminated. </p> <p>The only way to free resources
owned by the session is to explicitly close the session, or to terminate the
client process. Note that this makes it possible for a session to have no
client threads ! </p> </section>
<section id="GUID-9F7C4330-C524-4D8E-A78D-B519CF737D7D"><title>Message slots</title> <p>The maximum number of message slots
that can be allocated to a session, or the maximum number that can be dynamically
acquired from the system-wide pool, is 255. </p> </section>
</conbody></concept>