I did some more reading.
First, thanks for taking the time to write this. Its very helpful. Additional thoughts inline.
There could be value in refactoring things so as all the *Pending flags
of miscadmin.h get stored into one single volatile sig_atomic_t which
uses bit-wise markers, as that's at least 4 bytes because that's stored
as an int for most platforms and can be performed as an atomic operation
safely across signals (If my memory is right;) ). And this leaves a lot
of room for future flags.
Yeah I will look into this.
Ok so having looked into this a bit more....
It looks like to be strictly conforming, you can't just use a series of flags because neither C 89 or 99 guarantee that sig_atomic_t is read/write round-trip safe in signal handlers. In other words, if you read, are pre-empted by another signal, and then write, you may clobber what the other signal handler did to the variable. So you need atomics, which are C11....
What I would suggest instead at least for an initial approach is:
1. A struct of volatile bools statically stored
2. macros for accessing/setting/clearing flags
3. Consistent use of these macros throughout the codebase.
To make your solution work it looks like we'd need C11 atomics which would be nice and maybe at some point we decide to allow newer feature, or we could wrap this itself in checks for C11 features and provide atomic flags in the future. It seems that the above solution would strictly comply to C89 and pose no concurrency issues.
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Best Regards,
Chris Travers
Head of Database
Saarbrücker Straße 37a, 10405 Berlin