Date: Wed, 11 Oct 2017 10:13:35 +0100 From: Karl Pielorz <kpielorz_lst@tdx.co.uk> To: freebsd-hackers@freebsd.org Subject: fprintf - threadsafe? - i.e. with process linked against '-pthread'? Message-ID: <03DA6274A199550235DC7351@[10.12.30.106]>
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Hi, I have a number of 10.3-R amd64 boxes which runs a heavily threaded process. This is linked against '-pthread' - and compiles / runs fine. Using 'fprintf' to log data to a file - it sometimes doesn't complete writing the line - e.g. literally in code: fprintf( fd, "The quick brown %s jumped over the slow lazy animal\n", animal ); Will sometimes result in: " The quick brown fox ju" Being written to the file. Presumably (and from what I can see) fprintf is 'thread safe'? - And it also appears multiple threads could write to a single file using it (i.e. it provides for atomic writes so lines won't intermingle - the lines written don't seem to intermingle). The process doesn't crash - but I can't understand why / how frpintf could either stop, or get stopped 'mid way' through? e.g. If a signal occurred would it complete the write to file? This only happens very, very occasionally (one fprintf out of many millions, with hundreds of threads running). Just a bit stumped as to what to try looking at to fix / debug the problem - if anyone has any suggestions, or further reading I can look at. -Karl
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