m4_comment([$Id: appsignals.so,v 10.28 2002/02/23 20:05:24 bostic Exp $])m4_ref_title(Programmer Notes, Signal handling,    signal handling, apprec/config, program/errorret)m4_p([dnlWhen applications using m4_db receive signals, it is important that theyexit gracefully, discarding any m4_db locks that they may hold.  This isnormally done by setting a flag when a signal arrives and then checkingfor that flag periodically within the application.  Because m4_db is notre-entrant, the signal handler should not attempt to release locks and/orclose the database handles itself.  Re-entering m4_db is not guaranteed towork correctly, and the results are undefined.])m4_p([dnlIf an application exits holding a lock, the situation is no differentthan if the application crashed, and all applications participating inthe database environment must be shut down, and then recovery must beperformed.  If this is not done,  databases may be left in aninconsistent state, or locks the application held may cause unresolvabledeadlocks inside the environment, causing applications to hang.])m4_p([dnlm4_db restarts all system calls interrupted by signals, that is, anyunderlying system calls that return failure with errno set to EINTR willbe restarted rather than failing.])m4_page_footer