Non-volatile variables used for spinlock manipulation

Antonin Houska <ah@cybertec.at> writes:

Since SpinLockAcquire() / SpinLockRelease() macros usually reference variables
declared as volatile, I wonder if the following changes should be applied.

We've been making changes to remove that requirement, so I think that at
least in 9.5/HEAD this isn't an issue anymore.

regards, tom lane

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On 2015-09-04 09:42:20 -0400, Tom Lane wrote:

Antonin Houska <ah@cybertec.at> writes:

Since SpinLockAcquire() / SpinLockRelease() macros usually reference variables
declared as volatile, I wonder if the following changes should be applied.

We've been making changes to remove that requirement, so I think that at
least in 9.5/HEAD this isn't an issue anymore.

And even before that the pointer passed to SpinLockAcquire/Release()
didn't have to be volatile. The important thing was that read/writes
that are protected by the spinlock were only done via volatile
variables, to prevent them from being moved outside the critical
section. All the tas()/unlock section already force the pointer to the
lock to be volatile anyway.

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