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MINOR: h2: Document traps to be avoided on multithread.

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Document a few traps to avoid if we ever attempt to allow the upper layer
of the mux h2 to be run by multiple threads.
This commit is contained in:
Olivier Houchard 2019-10-11 16:33:49 +02:00 committed by Olivier Houchard
parent 06910464dd
commit 5a3671d8b1
1 changed files with 22 additions and 0 deletions
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22
src/mux_h2.c
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@ -1239,6 +1239,10 @@ static inline void h2s_close(struct h2s *h2s)
}
/* detaches an H2 stream from its H2C and releases it to the H2S pool. */
/* h2s_destroy should only ever be called by the thread that owns the stream,
* that means that a tasklet should be used if we want to destroy the h2s
* from another thread
*/
static void h2s_destroy(struct h2s *h2s)
{
struct connection *conn = h2s->h2c->conn;
@ -1261,9 +1265,14 @@ static void h2s_destroy(struct h2s *h2s)
*/
LIST_DEL_INIT(&h2s->list);
if (LIST_ADDED(&h2s->sending_list)) {
/* It should be OK to call tasklet_remove_from_tasklet_list()
* here, as only the thread responsible for the tasklet should
* be called here.
*/
tasklet_remove_from_tasklet_list(h2s->send_wait->tasklet);
LIST_DEL_INIT(&h2s->sending_list);
}
/* ditto, calling tasklet_free() here should be ok */
tasklet_free(h2s->wait_event.tasklet);
pool_free(pool_head_h2s, h2s);
@ -3809,6 +3818,11 @@ static void h2_detach(struct conn_stream *cs)
/* The stream is about to die, so no need to attempt to run its task */
if (LIST_ADDED(&h2s->sending_list) &&
h2s->send_wait != &h2s->wait_event) {
/*
* Calling tasklet_remove_from_tasklet_list() here is fine,
* as only the thread responsible for the tasklet should
* call h2_detach().
*/
tasklet_remove_from_tasklet_list(h2s->send_wait->tasklet);
LIST_DEL_INIT(&h2s->sending_list);
/*
@ -5628,6 +5642,9 @@ static int h2_unsubscribe(struct conn_stream *cs, int event_type, void *param)
/* We were about to send, make sure it does not happen */
if (LIST_ADDED(&h2s->sending_list) &&
h2s->send_wait != &h2s->wait_event) {
/* This call should be ok, as only the thread responsible
* for the tasklet should call unsubscribe.
*/
tasklet_remove_from_tasklet_list(h2s->send_wait->tasklet);
LIST_DEL_INIT(&h2s->sending_list);
}
@ -5720,6 +5737,11 @@ static void h2_stop_senders(struct h2c *h2c)
list_for_each_entry_safe(h2s, h2s_back, &h2c->sending_list, sending_list) {
LIST_DEL_INIT(&h2s->sending_list);
/* XXX: This won't work when/if streams are running on different
* threads, so we will have to find another way to prevent
* tasklets to run when we can no longer send data. The best
* may be to only wake enough tasklets to fill the buffer.
*/
tasklet_remove_from_tasklet_list(h2s->send_wait->tasklet);
h2s->send_wait->events |= SUB_RETRY_SEND;
}