On 01/05/2014 07:56 PM, Robert Haas wrote:
Right now, storing spinlocks in dynamic shared memory *almost* works, but there are problems with --disable-spinlocks. In that configuration, we use semaphores to simulate spinlocks. Every time someone calls SpinLockInit(), it's going to allocate a new semaphore which will never be returned to the operating system, so you're pretty quickly going to run out. There are a couple of things we could do about this:
5. Allocate a fixed number of semaphores, and multiplex them to emulate any number of spinlocks. For example, allocate 100 semaphores, and use the address of the spinlock modulo 100 to calculate which semaphore to use to emulate that spinlock.
That assumes that you never hold more than one spinlock at a time, otherwise you can get deadlocks. I think that assumptions holds currently, because acquiring two spinlocks at a time would be bad on performance grounds anyway.
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