Christian S.J. Peron 6a53f0a52b Revision 1.12 of lockf.c fixed a "thundering herd" scenario when the ... lock experienced contention a number of processes would race to acquire lock when it was released. This problem resulted in a lot of CPU load as well as locks being picked up out of order. Unfortunately, a regression snuck in which allowed multiple threads to pickup the same lock when -k was not used. This could occur when multiple processes open a file descriptor to inode X (one process will be blocked) and the file is unlinked on unlock (thereby removing the directory entry allow another process to create a new directory entry for the same file name and lock it). This changes restores the old algorithm of: wait for the lock, then acquire lock when we want to unlink the file on exit (specifically when -k is not used) and keeps the new algorithm for when -k is used, which yields fairness and improved performance. Also, update the man page to inform users that if lockf(1) is being used to facilitate concurrency between a number of processes, it is recommended that -k be used to reduce CPU load and yeld fairness with regard to lock ordering. Collaborated with: jdp PR: bin/114341 PR: bin/116543 PR: bin/111101 MFC after: 1 week		2007-10-12 14:56:52 +00:00
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lockf.1
lockf.c
Makefile