Practical TLA+ by Hillel Wayne

Author:Hillel Wayne
Language: eng
Format: epub
ISBN: 9781484238295
Publisher: Apress

For any two threads, they both can’t be in CS at the same time. We need the t1 /= t2 clause in there to make sure they’re different threads. Otherwise, TLC can pick the same thread as both t1 and t2.

In any case, let’s run the spec with Threads <- 1..2, INVARIANT AtMostOneCritical, Deadlock. The spec should fail with a deadlock after three steps. Both threads can turn on the flag at once. An early attempted solution was to have the flags enter a loop, constantly turning their own flag on and off until one of them gets into the critical section.fair process thread \in Threads

begin

P1: flag[self] := TRUE;

P2:

while \E t \in Threads \ {self}: flag[t] do

P2_1: flag[self] := FALSE;

P2_2: flag[self] := TRUE;

end while;

CS: skip;

P3: flag[self] := FALSE;

P4: goto P1;

end process;

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