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cvslock – Lock Repositories For Atomicity

Depends on: C compiler for installation; nothing for runtime

URL: ftp://riemann.iam.uni-bonn.de/pub/users/roessler/cvslock/

This program locks a CVS repository (either for reading or writing) in the same way that CVS does, so that CVS will honor the locks. This can be useful when, for example, you need to make a copy of the whole repository and want to avoid catching parts of commits or other people's lockfiles.

The cvslock distribution is packaged extremely well and can be installed according to the usual GNU procedures. Here's a transcript of an install session:

     floss$ zcat cvslock-0.1.tar.gz | tar xvf -
     cvslock-0.1/
     cvslock-0.1/Makefile.in
     cvslock-0.1/README
     cvslock-0.1/COPYING
     cvslock-0.1/Makefile.am
     cvslock-0.1/acconfig.h
     cvslock-0.1/aclocal.m4
     cvslock-0.1/config.h.in
     cvslock-0.1/configure
     cvslock-0.1/configure.in
     cvslock-0.1/install-sh
     cvslock-0.1/missing
     cvslock-0.1/mkinstalldirs
     cvslock-0.1/stamp-h.in
     cvslock-0.1/cvslock.c
     cvslock-0.1/cvslock.1
     cvslock-0.1/snprintf.c
     cvslock-0.1/cvslssh
     cvslock-0.1/VERSION
     floss$ cd cvslock-0.1
     floss$ ./configure
      ...
     floss$ make
     gcc -DHAVE_CONFIG_H -I. -I. -I.   -g -O2 -c cvslock.c
     gcc -g -O2  -o cvslock  cvslock.o
     floss$ make install
      ...
     floss$

(Note that you may have to do the make install step as root).

Now, cvslock is installed as /usr/local/bin/cvslock. When you invoke it, you can specify the repository with -d or via the $CVSROOT environment variable, just as with CVS itself (the following examples use -d). Its only required argument is the name of the directory to lock, relative to the top of the repository. That directory and all of its subdirectories will be locked. In this example, there are no subdirectories, so only one lockfile is created:

     floss$ ls /usr/local/newrepos/myproj/b-subdir/
     random.c,v
     floss$ cvslock -d /usr/local/newrepos  myproj/b-subdir
     floss$ ls /usr/local/newrepos/myproj/b-subdir/
     #cvs.rfl.cvslock.floss.27378  random.c,v
     floss$ cvslock -u -p 27378 -d /usr/local/newrepos  myproj/b-subdir
     floss$ ls /usr/local/newrepos/myproj/b-subdir/
     random.c,v
     floss$

Notice that when I cleared the lock (-u for unlock), I had to specify -p 27378. That's because cvslock uses Unix process IDs when creating lockfile names to ensure that its locks are unique. When you unlock, you have to tell cvslock which lock instance to remove, even if there's only one instance present. Thus, the -p flag tells cvslock which previous instance of itself it's cleaning up after (you can use -p with or without -u, though).

If you're going to be working in the repository for a while, doing various operations directly in the file system, you can use the -s option to have cvslock start up a new shell for you. It then consults the $SHELL environment variable in your current shell to determine which shell to use:

     floss$ cvslock -s -d /usr/local/newrepos myproj

The locks remain present until you exit the shell, at which time they are automatically removed. You can also use the -c option to execute a command while the repository is locked. Just as with -s, the locks are put in place before the command starts and removed when it's finished. In the following example, we lock the repository just long enough to display a listing of all of the lockfiles:

     floss$ cvslock -c 'find . -name "*cvslock*" ' -d /usr/local/newrepos myproj
     cvslock: '/usr/local/newrepos/myproj' locked successfully.
     cvslock: Starting 'find . -name "*cvslock*" -print'...
     ./a-subdir/subsubdir/#cvs.rfl.cvslock.floss.27452
     ./a-subdir/#cvs.rfl.cvslock.floss.27452
     ./b-subdir/#cvs.rfl.cvslock.floss.27452
     ./#cvs.rfl.cvslock.floss.27452
     floss$ find /usr/local/newrepos/myproj -name "*cvslock*" -print
     floss$

The command (the argument to the -c option) is run with the specified repository directory as its working directory.

By default, cvslock creates read-locks. You can tell it to use write-locks instead by passing the -W option. (You can pass -R to specify read-locks, but that's the default anyway.) Always remove any locks when you're finished, so that other users' CVS processes don't wait needlessly.

Note that cvslock must be run on the machine where the repository resides – you cannot specify a remote repository. (For more information, run man cvslock, which is a manual page installed when you ran make install.)

Karl Fogel wrote this book. Buy a printed copy via his homepage at red-bean.com

copyright  ©  September 18 2019 sean dreilinger url: https://durak.org/sean/pubs/software/cvsbook/cvslock-_002d_002d-Lock-Repositories-For-Atomicity.html