Removed unused spinlocks from DCBs, sessions and the MySQL protocol
structs. They were used in a context where only one thread has access to
the structure.
Removed unused member variables from DCBs.
This allows modules to only expose one entry point with a consistent
signature. In the future, this could be used to implement declarations of
module parameters.
- Rename session_getUser to session_get_user
- Change session_get_user and session_get_remote to take a const
SESSION* as argument and to return a const char*.
- Change server_get_persistent, so that user is passed as const.
- Update all users of these functions as appropriate.
Using the unique ID for the session is easier to use than an address. This
also allows the removal of all pointer values from the maxadmin output
which is never useful to the end user.
With the addition of filter capabilities, the tee filter should work with
all sorts of routers that require at most the RCAP_TYPE_CONTIGUOUS_INPUT
capability.
Due to a recent discovery of the server's capability to process multiple
requests, the filter can safely send data from one service to another
without waiting for the earlier replies.
This also fixes a minor problem with the cloning of DCBs where the backend
DCBs could end up in the wrong thread's pool.
Listeners are added to the list multiple times due to how DCBs are removed
from the list. This requires that an additional check is made so that we
are sure a DCB will not be added to the list twice.
When the client connections were listed, the DCB state was not
inspected. Only DCBs in the polling state should be printed as they are
guaranteed to be in a valid state.
The polling system now has a concept of messages. This can be used to send
a synchronous message to the polling system which waits for all threads to
process the message before returning.
Currently this is used to flush unused DCBs when server persistent
statistics are reported.
Making the lists of persistent DCBs thread specific is both a bug fix and
a performance enhancement. There was a small window where a non-owner
thread could receive events for a DCB. By partitioning the DCBs into
thread specific lists, this is avoided by removing the possibility of DCBs
moving between threads.
The `thread.next` pointer refers to active DCBs in the current thread's
list and the `memdata.next` pointer refers to DCBs about to be freed. The
latter was mixed up with the former due to some changes in the naming.
The code prevented scaling by imposing global spinlocks for the DCBs and
SESSIONs. Removing this list means that a thread-local list must be taken
into use to replace it.
The dcb_foreach allows a function to be mapped to all DCBs in
MaxScale. This allows the list of DCBs to be iterated in a safe manner
without having to worry about internal locking of the DCB mechanism.
Each DCB needs to be added to the owning thread's list so that they can be
iterated through. As sessions always have a client DCB, the sessions don't
need to be added to a similar per thread list.
This change fixes a problem with dcb_hangup_foreach that the removal of
the list manager introduced. Now the hangup events are properly injected
for the DCBs that connect to the server in question.
Since the listmanager code isn't used, the debug assertions will always
fail. They should be disabled until the listmanager code can converted to
the per-thread model.
Because each thread has their own epoll file descriptor and only one
thread can process a DCB, it makes sense to move to a per thread zombie
queue. This removes one of the last restrictions on scalability.
The listen() backlog is now set to INT_MAX which should guarantee that the
internal limit is always higher than the system limit. This means that the
length of the queue always follows /proc/sys/net/ipv4/tcp_max_syn_backlog.
