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or you don't understand what happens in my code when it runs on Linux. (Did you actually run it on a Linux system?)

No. I don't use Linux. And you're right. I did misinterpret what I saw in your post.

My main purpose was to point out:

The description of the Windows implementation of alarm was inadequate and somewhat misleading.
That the "polling" required to detect that the alarm signal (and other signals) had arrived, also occurs on Linux under the Safe Signals scheme.
See the PERL_ASYNC_CHECK() in run.c and Perl_despatch_signals(pTHX) in mg.c
See also perldoc/perlipc:

Long-running opcodes

As the Perl interpreter only looks at the signal flags when it is about to execute a new opcode, a signal that arrives during a long-running opcode (e.g. a regular expression operation on a very large string) will not be seen until the current opcode completes.

The rest was an attempt to understand (from your posted output) how linux was apparently able to interrupt flock when it appears to be implemented as a single opcode; and thus (according to my understanding of safe signals) should not be interruptible.

I don't understand why that works for you, unless you have PERL_SIGNALS=unsafe?

The (wrong) explanation I came up with seemed to fit; but then it is well passed the end of my (logical) day here and I'm somewhat punchy.

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority". I'm with torvalds on this

In the absence of evidence, opinion is indistinguishable from prejudice. Agile (and TDD) debunked

In reply to Re^6: Strawberry Perl and alarm() on Windows by BrowserUk
in thread Strawberry Perl and alarm() on Windows by bloonix

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Long-running opcodes