mirror of
http://git.haproxy.org/git/haproxy.git/
synced 2024-12-13 15:04:42 +00:00
42 lines
2.3 KiB
Plaintext
42 lines
2.3 KiB
Plaintext
2014/10/30 - dynamic buffer management
|
|
|
|
Since HTTP/2 processing will significantly increase the need for buffering, it
|
|
becomes mandatory to be able to support dynamic buffer allocation. This also
|
|
means that at any moment some buffer allocation will fail and that a task or an
|
|
I/O operation will have to be paused for the time needed to allocate a buffer.
|
|
|
|
There are 3 places where buffers are needed :
|
|
|
|
- receive side of a stream interface. A connection notifies about a pending
|
|
recv() and the SI calls the receive function to put the data into a buffer.
|
|
Here the buffer will have to be picked from a pool first, and if the
|
|
allocation fails, the I/O will have to temporarily be disabled, the
|
|
connection will have to subscribe for buffer release notification to be
|
|
woken up once a buffer is available again. It's important to keep in mind
|
|
that buffer availability doesn't necessarily mean a desire to enable recv
|
|
again, just that recv is not paused anymore for resource reasons.
|
|
|
|
- receive side of a stream interface when the other end point is an applet.
|
|
The applet wants to write into the buffer and for this the buffer needs to
|
|
be allocated as well. It is the same as above except that it is the applet
|
|
which is put to a pause. Since the applet might be at the core of the task
|
|
itself, it could become tricky to handle the situation correctly. Stats and
|
|
peers are in this situation.
|
|
|
|
- Tx of a task : some tasks perform spontaneous writes to a buffer. Checks
|
|
are an example of this. The checks will have to be able to sleep while a
|
|
buffer is being awaited.
|
|
|
|
One important point is that such pauses must not prevent the task from timing
|
|
out. There it becomes difficult because in the case of a time out, we could
|
|
want to emit a timeout error message and for this, require a buffer. So it is
|
|
important to keep the ability not to send messages upon error processing, and
|
|
to be able to give up and stop waiting for buffers.
|
|
|
|
The refill mechanism needs to be designed in a thread-safe way because this
|
|
will become one of the rare cases of inter-task activity. Thus it is important
|
|
to ensure that checking the state of the task and passing of the freshly
|
|
released buffer are performed atomically, and that in case the task doesn't
|
|
want it anymore, it is responsible for passing it to the next one.
|
|
|