From cacff1be886ed975bbef1b17151b25c633711256 Mon Sep 17 00:00:00 2001 From: Eelco Dolstra Date: Mon, 23 Mar 2009 01:05:54 +0000 Subject: * No longer block while waiting for a lock on a store path. Instead poll for it (i.e. if we can't acquire the lock, then let the main select() loop wait for at most a few seconds and then try again). This improves parallelism: if two nix-store processes are both trying to build a path at the same time, the second one shouldn't block; it should first see if it can build other goals. Also, it prevents the deadlocks that have been occuring in Hydra lately, where a process waits for a lock held by another process that's waiting for a lock held by the first. The downside is that polling isn't really elegant, but POSIX doesn't provide a way to wait for locks in a select() loop. The only solution would be to spawn a thread for each lock to do a blocking fcntl() and then signal the main thread, but that would require pthreads. --- src/libstore/pathlocks.hh | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'src/libstore/pathlocks.hh') diff --git a/src/libstore/pathlocks.hh b/src/libstore/pathlocks.hh index 9898b497b94d..64d62f6ae899 100644 --- a/src/libstore/pathlocks.hh +++ b/src/libstore/pathlocks.hh @@ -33,8 +33,9 @@ public: PathLocks(); PathLocks(const PathSet & paths, const string & waitMsg = ""); - void lockPaths(const PathSet & _paths, - const string & waitMsg = ""); + bool lockPaths(const PathSet & _paths, + const string & waitMsg = "", + bool wait = true); ~PathLocks(); void unlock(); void setDeletion(bool deletePaths); -- cgit 1.4.1