Locking Files

tcov uses a simple file-locking mechanism for updating the block coverage database in the .d files. It employs a single file, /tmp/tcov.lock, for this purpose. Consequently, only one executable compiled with -xa (C) or -a (other compilers) should be running on the system. If the execution of the program compiled with the -xa (or -a) option is manually terminated, then the /tmp/tcov.lock file must be deleted manually.

Files compiled with the -xa or -a option call the profiling tools subroutines automatically when a program is linked for tcov profiling. At program exit, these subroutines combine the information collected at runtime for file xyz.f with the existing profiling information stored in file xyz.d. To ensure this information is not corrupted by several people simultaneously running a profiled binary, a xyz.d.lock lock file is created for xyz.d for the duration of the update. If there are any errors in opening or reading xyz.d or its lock file, or if there are inconsistencies between the runtime information and the stored information, then the information stored in xyz.d is not changed.

An edit and recompile of xyz.d may change the number of counters in xyz.d. This is detected if an old profiled binary is run.

If too many people are running a profiled binary, the lock cannot be obtained. An error message similar to the following is displayed after a delay of several seconds:

tcov_exit: Failed to create lock file '/tmp_mnt/net/rbbb/export/home/src/newpattern/foo.d.lock' for coverage data file '/tmp_mnt/net/rbbb/export/home/src/newpattern/foo.d' after 5 tries. Is somebody else running this binary?

The stored information is not updated. This locking is safe across a network. Since locking is performed on a file-by-file basis, other files may be correctly updated.

The profiling subroutines attempt to deal with automounted file systems that have become inaccessible. They still fail if the file system containing a coverage data file is mounted with different names on different machines, or if the user running the profiled binary does not have permission to write to either the coverage data file or the directory containing it. Be sure all the directories are uniformly named and writable by anyone expected to run the binary.