speedtables startup locking sometimes fails to provide mutual exclusion / fails outright

[mutability]

If you start up a few separate processes concurrently that share the same table definition (and working area) sometimes the locking during table init fails outright like this:

error deleting "/var/tmp/adsb/c_aircraft_registry_faa.lock.lock": no such file or directory
    while executing
"file delete $name.lock"
    (procedure "unlockfile" line 20)
    invoked from within
"unlockfile $lockfile"
    (procedure "lockfile" line 71)
    invoked from within
"lockfile $build_dir err"
    (procedure "::stapi::init_ctable" line 30)
    invoked from within
"::stapi::init_ctable aircraft_registry_faa "" "modescode IS NOT NULL AND active IS TRUE" modescode nnumber"
    (procedure "create_stapi_tables" line 12)
    invoked from within
"create_stapi_tables"
    (procedure "main" line 88)
    invoked from within

Additionally, sometimes in the same sort of situation, compilation will fail with bizarre errors because there are two processes trying to compile in the same place (i.e. the locking is not providing mutual exclusion).

[mutability]

It looks like lockfile is fundamentally broken. It assumes that tcl's "file rename" without -force is atomic, i.e. it will either rename the file without clobbering, or fail.

This is not true. It first checks if the target exists. If the target does not exist, then it does a rename() call, which atomically replaces the target if it exists. There is a window between the test and the rename where another process could create the lockfile.

I'd suggest just using TclX's "flock" (open the lockfile in a+ mode, try to flock -nowait, keep the lockfile open until you want to release the lock)

[mutability]

or you could probably do something with opening the lockfile with flags CREAT EXCL

[resuna]

I've created a "locking" branch off "stapi-test" to work on this. Creating the lockfile directly creates a potential race condition where the lockfile is created but the PID of the opener hasn't been put into it. I think I've handled that. Can you give it a try?

[bovine]

Fixed in 1.6.4 release.