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Further to my post from yesterday, I'm finding out that what I'm trying to do may not be possible.

In short, I am trying to call a potentially long running process (Ghostscript) that is wrapped in some code that sets an alarm, then does an eval to call Ghostscript. Either Ghostscript finishes, or the alarm triggers to catch a runaway page being rendered.

My apache says:

[alex@foo bar]$ sudo /usr/sbin/httpd -V
Server version: Apache/2.0.40
Server built:   Nov 27 2003 11:04:06
Server's Module Magic Number: xxxxxxxx:x
Architecture:   32-bit
Server compiled with....
 -D APACHE_MPM_DIR="server/mpm/prefork"
 -D APR_HAS_SENDFILE
 -D APR_HAS_MMAP
 -D APR_HAVE_IPV6
 -D APR_USE_SYSVSEM_SERIALIZE
 -D APR_USE_PTHREAD_SERIALIZE
 -D SINGLE_LISTEN_UNSERIALIZED_ACCEPT
 -D APR_HAS_OTHER_CHILD
 -D AP_HAVE_RELIABLE_PIPED_LOGS
 -D HTTPD_ROOT="/etc/httpd"
 -D SUEXEC_BIN="/usr/sbin/suexec"
 -D DEFAULT_PIDLOG="logs/httpd.pid"
 -D DEFAULT_SCOREBOARD="logs/apache_runtime_status"
 -D DEFAULT_LOCKFILE="logs/accept.lock"
 -D DEFAULT_ERRORLOG="logs/error_log"
 -D AP_TYPES_CONFIG_FILE="conf/mime.types"
 -D SERVER_CONFIG_FILE="conf/httpd.conf"
[download]

I'm not sure if there's anything else on my system that I should be checking.

I've done testing using sudo strace /usr/sbin/httpd -f /home/foo/bar/conf/httpd.conf -X and things seem to go bad as soon as the alarm is set ..

...
getgroups32(0x20, 0xbfffeab0)           = 1
rt_sigaction(SIGALRM, {0x4044fc80, [], SA_RESTORER, 0x402b88f8}, {SIG_
+DFL}, 8) = 0
time(NULL)                              = 1164821271
alarm(602)                              = 0
pipe([9, 10])                           = 0
ioctl(9, SNDCTL_TMR_TIMEBASE, 0xbfffe970) = -1 EINVAL (Invalid argumen
+t)
_llseek(9, 0, 0xbfffe9c0, SEEK_CUR)     = -1 ESPIPE (Illegal seek)
ioctl(10, SNDCTL_TMR_TIMEBASE, 0xbfffe970) = -1 EINVAL (Invalid argume
+nt)
_llseek(10, 0, 0xbfffe9c0, SEEK_CUR)    = -1 ESPIPE (Illegal seek)
fcntl64(9, F_SETFD, FD_CLOEXEC)         = 0
fcntl64(10, F_SETFD, FD_CLOEXEC)        = 0
pipe([11, 12])                          = 0
ioctl(11, SNDCTL_TMR_TIMEBASE, 0xbfffe970) = -1 EINVAL (Invalid argume
+nt)
_llseek(11, 0, 0xbfffe9c0, SEEK_CUR)    = -1 ESPIPE (Illegal seek)
ioctl(12, SNDCTL_TMR_TIMEBASE, 0xbfffe970) = -1 EINVAL (Invalid argume
+nt)
_llseek(12, 0, 0xbfffe9c0, SEEK_CUR)    = -1 ESPIPE (Illegal seek)
fcntl64(11, F_SETFD, FD_CLOEXEC)        = 0
fcntl64(12, F_SETFD, FD_CLOEXEC)        = 0
...
[download]

Naturally, I googled for this problem and came up with this post which points to this post which actually contains some really interesting discussion. The post in that thread that seems to sum things up is this one, but this isn't 100% decided. This post later in the thread says

3rd party Apache 2 modules should avoid using code relying on signals. This is because typical signal use is not thread-safe and modules which rely on signals may not work portably. Certain signals may still work for non-threaded mpms. For example alarm() can be used under prefork MPM, but it won't work on any other MPM. Moreover Apache can't guarantee that the signals that currently happen to work will continue to do so in the future Apache releases. So use them at your own risk.

So it may be that I can't use alarms to catch runaway code after all.

Has anyone here had experience using alarms under Apache2?

Alex / talexb / Toronto

"Groklaw is the open-source mentality applied to legal research" ~ Linus Torvalds

In reply to mod_perl, prefork mpm and alarms by talexb

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