forked from lix-project/lix
cacff1be88
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.
52 lines
1.1 KiB
C++
52 lines
1.1 KiB
C++
#ifndef __PATHLOCKS_H
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#define __PATHLOCKS_H
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#include "types.hh"
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namespace nix {
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/* Open (possibly create) a lock file and return the file descriptor.
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-1 is returned if create is false and the lock could not be opened
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because it doesn't exist. Any other error throws an exception. */
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int openLockFile(const Path & path, bool create);
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/* Delete an open lock file. Both must be called to be fully portable
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between Unix and Windows. */
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void deleteLockFilePreClose(const Path & path, int fd);
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void deleteLockFilePostClose(const Path & path);
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enum LockType { ltRead, ltWrite, ltNone };
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bool lockFile(int fd, LockType lockType, bool wait);
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class PathLocks
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{
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private:
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typedef std::pair<int, Path> FDPair;
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list<FDPair> fds;
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bool deletePaths;
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public:
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PathLocks();
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PathLocks(const PathSet & paths,
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const string & waitMsg = "");
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bool lockPaths(const PathSet & _paths,
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const string & waitMsg = "",
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bool wait = true);
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~PathLocks();
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void unlock();
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void setDeletion(bool deletePaths);
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};
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bool pathIsLockedByMe(const Path & path);
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}
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#endif /* !__PATHLOCKS_H */
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