A mechanism that I considered some time ago but never implemented might serve you. If your main log file is called /path/to/logfile, then your processes could write to /path/to/logfile.$$ where $$ is their PID. Each process would have their own log file, so no problems locking. These individual files could then be merged into /path/to/logfile at a more convenient time.

Failing that, Log::Log4Perl is highly recommended.