I have tried to use the RTS thread packages with MySQL but stumbled on the following problems:
They use old versions of many POSIX calls and it is very tedious to make wrappers for all functions. I am inclined to think that it would be easier to change the thread libraries to the newest POSIX specification.
Some wrappers are currently written. See
mysys/my_pthread.c for more info.
At least the following should be changed:
pthread_get_specific should use one argument.
sigwait should take two arguments. A lot of
functions (at least
pthread_cond_timedwait()) should return the
error code on error. Now they return -1 and set
Another problem is that user-level threads use the
ALRM signal and this aborts a lot of functions
open...). MySQL should do a retry on interrupt
on all of these but it is not that easy to verify it.
The biggest unsolved problem is the following:
To get thread-level alarms I changed
mysys/thr_alarm.c to wait between alarms with
pthread_cond_timedwait(), but this aborts with
EINTR. I tried to debug the thread
library as to why this happens, but couldn't find any easy
If someone wants to try MySQL with RTS threads I suggest the following:
Change functions MySQL uses from the thread library to POSIX. This shouldn't take that long.
Compile all libraries with the
If there are some small differences in the implementation,
they may be fixed by changing
thr_alarm. If it runs without any
“warning,” “error,” or aborted
messages, you are on the right track. Here is a successful run
Main thread: 1 Thread 0 (5) started Thread: 5 Waiting process_alarm Thread 1 (6) started Thread: 6 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 1 (1) sec Thread: 6 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 2 (2) sec Thread: 6 Simulation of no alarm needed Thread: 6 Slept for 0 (3) sec Thread: 6 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 4 (4) sec Thread: 6 Waiting process_alarm thread_alarm Thread: 5 Slept for 10 (10) sec Thread: 5 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 5 (5) sec Thread: 6 Waiting process_alarm process_alarm ... thread_alarm Thread: 5 Slept for 0 (1) sec end
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