(this can be used for general discussion of per-thread data)
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[CMcC] Each of the following [tcl core subsystems] contains Thread Specific Data:

    * tclFileName
    * tclIO ([Tcl Core IO System])
    * tclNotify
    * tclAsync
    * tclEvent
    * tclTimer
    * and even tclRegexp

It's used, somewhat like ClientData, to store per-thread quasi-global arbitrary data,
which is required to maintain state, and used to clean up on termination
or [Finalization] as it is called in the [tcl core]

This is useful, because it helps modularise each subsystem, however the very encapsulation
makes it impossible to extend or modify the subsystems additively, which would make it easier to
test subsystem mods without pulling apart entire subsystems.

I'm writing a TIP on this subject.

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[LV] In Jan, 2007, on the [starkit] mailing list, a user asked about problems
between [thread]s and [vfs]. [JH] replied that vfs mount points are not
shared between threads by design to try to limit easy crash conditions.
If a particular vfs mount point is needed, it should be mounted within
the thread.

As with all packages, once loaded in any interp, they are available 
statically to all others.

 hobbit [~] 4 % /Library/Tcl/basekits/base-tcl-thread-macosx-universal
 % package require Thread
 2.6.5
 % set t [thread::create {thread::wait}]
 tid0x1804e00
 % package require vfs
 1.3
 % thread::send $t {load {} vfs}
 % thread::send $t {package names}
 Thread tclkitpath zlib vfs Mk4tcl Tcl


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[Category Threads]