note 108270 added to splfileobject.flock

It's important to note that digitalprecision's assertion that the ftruncate() call is redundant is not true. It is necessary. The fopen call (in this case the SplFileObject constructor) will truncate the file, but there's a race condition similar to the following (ignoring buffering and such for a moment): Process A: fopen("somefile.txt", "w") Process A: fwrite("line 1\n") Process B: fopen("somefile.txt", "w") Process A: fwrite("line 2\n") Process A: fclose() Process B: flock(LOCK_EX) Process B: fwrite("exclusive line 1\n"); Process B: flock(LOCK_UN) Process B: fclose() Expected File Contents: exclusive line 1 Actual File Contents: line 2 exclusive line 1 If the file is written to by another process between the open call and the lock call, there will be unexpected data at the beginning of the file. This is why the truncate call is needed after an exclusive lock is obtained. ---- Server IP: 64.71.164.2 Probable Submitter: 166.108.254.215 ---- Manual Page -- http://www.php.net/manual/en/splfileobject.flock.php Edit -- https://master.php.net/note/edit/108270 Del: integrated -- https://master.php.net/note/delete/108270/integrated Del: useless -- https://master.php.net/note/delete/108270/useless Del: bad code -- https://master.php.net/note/delete/108270/bad+code Del: spam -- https://master.php.net/note/delete/108270/spam Del: non-english -- https://master.php.net/note/delete/108270/non-english Del: in docs -- https://master.php.net/note/delete/108270/in+docs Del: other reasons-- https://master.php.net/note/delete/108270 Reject -- https://master.php.net/note/reject/108270 Search -- https://master.php.net/manage/user-notes.php