https://issues.apache.org/SpamAssassin/show_bug.cgi?id=6028
Summary: Logger in infinite loop when logging encounters an error
Product: Spamassassin
Version: SVN Trunk (Latest Devel Version)
Platform: All
OS/Version: All
Status: NEW
Severity: normal
Priority: P5
Component: Libraries
AssignedTo: [email protected]
ReportedBy: [EMAIL PROTECTED]
I'm opening this PR to explain my change r724958 (
https://svn.apache.org/viewcvs.cgi?view=rev&rev=724958 ).
The immediate problem the change solves is that a command-line
'spamassassin -D' when piping its stderr and stdout into another
program like more(1) or less(1) can enter an infinite loop
when a pipe breaks.
In my particular case I admit the problem was caused by my
addition of a call to 'warn' in Logger::Stderr::log_message,
so if print failed a warn was called, which was intercepted
by a __WARN__ handler and log_message called again.
Several solutions come to mind:
- ban calling warn or die or dbg from any routine that may be
called from Logger::log_message. That is doable, but requires
some discipline, and if a caller supplies his own logging
modules we still have no control over it;
- override __WARN__ and __DIE__ handlers within Logger::log_message
- or like I did, add a flag (poor man semaphore) to protect
the inside of Logger::log_message from re-entering.
Probably the #2 is cleanest, but I thought testing and flipping
a single boolean scalar is the cheapest, so I chose #3.
I also added a:
local $SIG{PIPE} = 'IGNORE';
into Logger::Stderr::log_message to prevent broken pipe signalling,
but I'm now considering reverting that change because is is not
particularly lightweight, involving several system service calls.
I see that sa-learn.raw and spamassassin.raw already neutralize
the PIPE signal, so it is unnecessary to do it again in logger,
although I'm not sure about other callers (spamd, mass-check,
third-party code).
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