tvl-depot/src/libstore/pathlocks.hh
Eelco Dolstra cacff1be88 * 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.
2009-03-23 01:05:54 +00:00

51 lines
1.1 KiB
C++

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