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Added spinlock protection for the session association to the DCB and

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reworked the reference count mechanism on the session.  Introduced a
FREE state for the session and alter the session destruction flow so
that we only remove the session when all the DCB's have singled they
have finished processing events for the DCB rather than when the first
thread decides to clsoe the DCB.
This commit is contained in:
Mark Riddoch
2013-09-04 12:24:59 +02:00
parent 8debc4433c
commit f74f67540f
5 changed files with 76 additions and 43 deletions
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60
server/core/session.c
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@ -78,7 +78,6 @@ session_alloc(SERVICE *service, DCB *client)
return NULL;
}
session->refcount = 0;
session->ses_chk_top = CHK_NUM_SESSION;
session->ses_chk_tail = CHK_NUM_SESSION;
@ -94,15 +93,26 @@ session_alloc(SERVICE *service, DCB *client)
session->stats.connect = time(0);
session->state = SESSION_STATE_ALLOC;
/**
* If client has data pointer to authentication info, set it to session.
* Associate the session to the client DCB and set the reference count on
* the session to indicate that there is a single reference to the session.
* There is no need to protect this or use atomic add as the session has not
* been made available to the other threads at this point.
*/
session->data = client->data;
client->session = session;
session->refcount = 1;
/** Release session lock */
spinlock_release(&session->ses_lock);
/*
* Only create a router session if we are not the listening
* DCB. Creating a router session may create a connection to a
* backend server, depending upon the router module implementation
* and should be avoided for the listener session
*
* Router session creation may create other DCBs that link to the
* session, therefore it is important that the session lock is relinquished
* beforethe router call.
*/
if (client->state != DCB_STATE_LISTENING)
{
@ -116,8 +126,6 @@ session_alloc(SERVICE *service, DCB *client)
/** This indicates that session is ready to be shared with backend DCBs. */
session->state = SESSION_STATE_READY;
/** Release session lock */
spinlock_release(&session->ses_lock);
atomic_add(&service->stats.n_sessions, 1);
atomic_add(&service->stats.n_current, 1);
@ -125,6 +133,28 @@ session_alloc(SERVICE *service, DCB *client)
return session;
}
/**
* Link a session to a DCB.
*
* @param session The session to link with the dcb
* @param dcb The DCB to be linked
* @return True if the session was sucessfully linked to the DCB
*/
bool
session_link_dcb(SESSION *session, DCB *dcb)
{
spinlock_acquire(&session->ses_lock);
if (session->state == SESSION_STATE_FREE)
{
spinlock_release(&session->ses_lock);
return false;
}
atomic_add(&session->refcount, 1);
dcb->session = session;
spinlock_release(&session->ses_lock);
return true;
}
/**
* Deallocate the specified session
*
@ -134,9 +164,24 @@ void
session_free(SESSION *session)
{
SESSION *ptr;
CHK_SESSION(session);
spinlock_acquire(&session->ses_lock);
if (atomic_add(&session->refcount, -1) > 1)
{
/*
* There are still other references to the session
* so we simply return after decrementing the session
* count.
*/
spinlock_release(&session->ses_lock);
return;
}
session->state = SESSION_STATE_FREE;
spinlock_release(&session->ses_lock);
/* First of all remove from the linked list */
spinlock_acquire(&session_spin);
if (allSessions == session)
{
@ -156,10 +201,7 @@ SESSION *ptr;
atomic_add(&session->service->stats.n_current, -1);
/* Clean up session and free the memory */
if (atomic_add(&session->refcount, -1) == 1)
{
free(session);
}
free(session);
}
/**