E.4. Comments about RTS Threads
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_wait,
pthread_cond_timedwait()) should return the
error code on error. Now they return -1 and set
errno.
Another problem is that user-level threads use the
ALRM signal and this aborts a lot of functions
(read, write,
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
error EINTR. I tried to debug the thread
library as to why this happens, but couldn't find any easy
solution.
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
-DHAVE_rts_threads.
Compile thr_alarm.
If there are some small differences in the implementation,
they may be fixed by changing
my_pthread.h and
my_pthread.c.
-
Run thr_alarm. If it runs without any
“warning,” “error,” or aborted
messages, you are on the right track. Here is a successful run
on Solaris:
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
