On Friday 19 November 2010 15:38:37 Robert Haas wrote: > Eh, really? If there's a workaround for platforms for which we don't > know what the appropriate read-fencing incantation is, then I'd feel > more comfortable about doing this. But I don't see how to make that > work. The whole problem here is that API is designed in such a way > that the signal handler might be invoked when the lock that it needs > to grab is already held by the same process. The reason memory > barriers solve the problem is because they'll be atomically released > when we jump into the signal handler, but that is not true of a > spin-lock or a semaphore. Well, its not generally true - you are right there. But there is a wide range for syscalls available where its inherently true (which is what I sloppily referred to). And you are allowed to call a, although quite restricted, set of system calls even in signal handlers. I don't have the list for older posix versions in mind, but for 2003 you can choose something from several like write, lseek,setpgid which inherently have to serialize. And I am quite sure there were sensible calls for earlier versions.
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