Hi Jan.
> Time-of-check_to_time-of-use
Yes, that's the underlying problem and that's why I used TryLock() to start
with. It resolves the problem atomically. I would imagine that it determines
if the mutex is locked, then locks it regardless, by doing something like a
"swap". But by itself that isn't useful. It also returns the prior state of
the mutex. Thus, the user knows both the prior state and the current state.
The only exception I can think of would be if a TryUnlock() was used after it -
and perhaps that's why Go chose to just offer the one and not both.
The "if" inside TryUnlock() is acting on "time-of-check" information, and the
mutex has been locked since then, and still is when TryUnlock()'s Unlock()
executes.
I think that this might be less confusing if we can all agree that the
description of TryLock() was enhanced a bit. Instead of:
"TryLock tries to lock m and reports whether it succeeded."
I take "succeed" to mean that TryLock() found the lock unset, and set it. The
opposite, to "fail" means that TryLock() found the lock set, so didn't have to
set it.
If so, I think this description would be clearer.
"TryLock reports success if it locks m, else failure due to m being already
locked. Either way, m ends up being locked.
If we can agree to this much about TryLock()'s behavior, then consider that in
my proposed TryUnlock(), action is only taken when my code verified that the
mutex was unlocked to start with, and at that same time it was locked. So now
I can safely execute an Unlock().
John
John Souvestre New Orleans LA, USA 504-454-0899
-----Original Message-----
From: Jan Mercl <[email protected]>
Sent: 2026-01-05, Mon 12:12
To: John Souvestre <[email protected]>
Cc: Bushnell, Thomas <[email protected]>; [email protected]
Subject: Re: [go-nuts] TryUnlock() and IsLocked() functions
On Mon, Jan 5, 2026 at 7:10 PM 'John Souvestre' via golang-nuts
<[email protected]> wrote:
> So you are saying that TryLock()’s return (succeeded or failed) might not be
> correct?
See https://en.wikipedia.org/wiki/Time-of-check_to_time-of-use
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