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
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