Threads and lexical scope

Threads and lexical scope

[Panicz Maciej Godek]

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Hi,
I've been investigating the behaviour of threads created in the same
lexical scope, and I have to admit that I'm a little puzzled.
The documentation states, that the "call-with-new-thread" procedure calls
its argument in a new thread and with a new dynamic state, the latter being
described in more detail with the introduction of the notion of fluids.

Nothing is being said regarding the behaviour of new thread with respect to
the current lexical scope.

The test program below shows, that each thread obtains its own copy of a
current lexical scope:

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Re: Threads and lexical scope

[Panicz Maciej Godek]

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(sorry, I accidentally pressed ctrl+return, which caused my mail client to
send the message).
So here's the code:

(for-each
    (lambda(i)
      (let ((thread (call-with-new-thread
                     (lambda ()
                       (sleep (+ (random 10) 2))
                       (format #t "woke ~a: ~a\n" (current-thread) i)))))
        (format #t "created ~a: ~a\n" thread i)))
    (iota 5))

It displays something like this (with the "woke" messages being displayed
at some random instances of time, of course):

created #<thread 140077961983744 (d57000)>: 0
created #<thread 140077970376448 (e36400)>: 1
created #<thread 140077978769152 (e40c00)>: 2
created #<thread 140077995554560 (e40a00)>: 3
created #<thread 140077987161856 (e40800)>: 4
woke #<thread 140077970376448 (e36400)>: 1
woke #<thread 140077961983744 (d57000)>: 0
woke #<thread 140077978769152 (e40c00)>: 2
woke #<thread 140077995554560 (e40a00)>: 3
woke #<thread 140077987161856 (e40800)>: 4

So it seems that each thread keeps the value of the variable from the
moment of its creation. This is fine (and perhaps that's the most
reasonable behaviour), but I'm a little worried that I didn't manage to
find it in the documentation, so I'm just writing to receive confirmation ;]

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Re: Threads and lexical scope

[Panicz Maciej Godek]

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Oh, I just realized that each thread was created in a new closure anyway,
so they weren't able to share the variable. Sorry for the confusion.

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Re: Threads and lexical scope

[Panicz Maciej Godek]

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2014/1/14 Panicz Maciej Godek <godek.maciek@gmail.com>

> Oh, I just realized that each thread was created in a new closure anyway,
> so they weren't able to share the variable. Sorry for the confusion.
>

It was a confusion, because the lexical scopes of threads are obviously
shared.

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