Re: [Tarantool-patches] [PATCH] Add a cancellation guard to cpipe flush callback

[Leonid Vasiliev <lvasiliev@tarantool.org>]

On 12/23/19 3:55 PM, Konstantin Osipov wrote:
> * Leonid Vasiliev <lvasiliev@tarantool.org> [19/12/23 15:48]:
>> +	while(hang_endpoint.mutex.__data.__lock < 2) {
>> +		usleep(100);
>> +	}
> 
> How does this work? Is there a way to not look inside mutex?
> 

Other alternatives (which I can come up with) add possible races or 
cancellation points.
We must cancel the thread before cancellation point in ev_async_send
(ev_async_send(endpoint->consumer, &endpoint->async);) and as close as 
possible to it for to reproduce a behavior from 
https://github.com/tarantool/tarantool/issues/4127 .

How it's work (it's hack):
mutex.__data.__lock == 0 - mutex unlocked
mutex.__data.__lock == 1 - mutex locked
mutex.__data.__lock == 2 - waiters are exists

We just wait while the canceled worker try to lock the endpoint mutex
and cancelate thread at the moment. if you have any ideas how this can 
be done better and without possible races, tell me.
And yes, I must to disable this dirty test for OSes other than Linux.

---
diff --git a/test/unit/CMakeLists.txt b/test/unit/CMakeLists.txt
index 339521489..fb8f74be0 100644
--- a/test/unit/CMakeLists.txt
+++ b/test/unit/CMakeLists.txt
@@ -98,8 +98,10 @@ target_link_libraries(cbus_stress.test core stat)
  add_executable(cbus.test cbus.c)
  target_link_libraries(cbus.test core unit stat)

-add_executable(cbus_hang.test cbus_hang.c)
-target_link_libraries(cbus_hang.test core unit stat)
+if (${CMAKE_HOST_SYSTEM_NAME} MATCHES "Linux")
+    add_executable(cbus_hang.test cbus_hang.c)
+    target_link_libraries(cbus_hang.test core unit stat)
+endif ()