The Fortress Language Specification - CiteSeerX

stop exception and transforms it into a deferred Stopped exception. This is visible to the programmer and should be
caught by invoking the val method on the thread object. Implicit threads are terminated only if another thread in the
group completes abruptly, and the threads that are terminated are ignored for the purposes of the completion of the
group.
Typical code for stopping a thread looks something like the following example:
x : Z64 := 0
t = spawn do
try
atomic if x = 0 then abort() else () end
finally
x := 1
end
end
t.stop()
try
t.val()
catch s
Stopped ⇒ x += 2; x
end
Here the spawned thread t blocks until it is killed by the call to t.stop() ; it sets x to 1 in the finally clause before
exiting. In this case, the call to t.val() will throw Stopped, which is caught, causing 2 to be added to x and returning
3.
Note that there is a race in the above code, so the try block in t may not have been entered when t.stop() is called,
causing x to be 2 at the end of execution. Note also that the call to t.stop() occurs asynchronously; in the absence of
the call to t.val() , the spawning thread would not have waited for t to complete.
32.7 Placing Threads
A thread can be placed in a particular region by using an at expression:
(v, w) = (a i ,
at a.region(j) do
a j
end)
In this example, two implicit threads are created; the first computes a i locally, the second computes a j in the region
where the j th element of a resides, specified by a.region(j) . The expression after at must return a value of type
Region, and the block immediately following do is run in that region; the result of the block is the result of the at
expression as a whole. Often it is more graceful to use the also do construct (described in Section 13.12) in these
cases:
do
v := a i
alsoat a.region(j) do
w := a j
end
We can also use at with a spawn expression:
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