Re: [PATCH 1/2] aio: allow to wait for coroutine pool from different coroutine

[Vladimir Sementsov-Ogievskiy]

10.06.2020 17:41, Denis V. Lunev wrote:

The patch preserves the constraint that the only waiter is allowed.

Signed-off-by: Denis V. Lunev <d...@openvz.org>
CC: Kevin Wolf <kw...@redhat.com>
CC: Max Reitz <mre...@redhat.com>
CC: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
CC: Denis Plotnikov <dplotni...@virtuozzo.com>
---
  block/aio_task.c | 8 ++++----
  1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/block/aio_task.c b/block/aio_task.c
index 88989fa248..f338049147 100644
--- a/block/aio_task.c
+++ b/block/aio_task.c
@@ -27,7 +27,7 @@
  #include "block/aio_task.h"

struct AioTaskPool {

-    Coroutine *main_co;
+    Coroutine *wake_co;
      int status;
      int max_busy_tasks;
      int busy_tasks;
@@ -54,15 +54,15 @@ static void coroutine_fn aio_task_co(void *opaque)

if (pool->waiting) {

          pool->waiting = false;
-        aio_co_wake(pool->main_co);
+        aio_co_wake(pool->wake_co);
      }
  }

void coroutine_fn aio_task_pool_wait_one(AioTaskPool *pool)

  {
      assert(pool->busy_tasks > 0);
-    assert(qemu_coroutine_self() == pool->main_co);

+ pool->wake_co = qemu_coroutine_self();

      pool->waiting = true;
      qemu_coroutine_yield();

@@ -98,7 +98,7 @@ AioTaskPool *coroutine_fn aio_task_pool_new(int max_busy_tasks)

  {
      AioTaskPool *pool = g_new0(AioTaskPool, 1);

- pool->main_co = qemu_coroutine_self();

+    pool->wake_co = NULL;
      pool->max_busy_tasks = max_busy_tasks;

return pool;

With such approach, if several coroutines will wait simultaneously, the only 
one will be finally woken and other will hang.

I think, we should use CoQueue here: CoQueue instead of wake_co, 
qemu_co_queue_wait in wait_one, and qemu_co_queue_next instead of aio_co_wake.


--
Best regards,
Vladimir