cbeaa91dbb Update ValidationInterface() documentation to explicitly specify threading and memory model (Jesse Cohen)
b296b425a7 Update documentation for SingleThreadedSchedulerClient() to specify the memory model (Jesse Cohen)
9994d01d8b Add Unit Test for SingleThreadedSchedulerClient (Jesse Cohen)
Pull request description:
As discussed in #13023 I've split this test out into a separate pr
This test (and documentation update) makes explicit the guarantee (previously undefined, but implied by the 'SingleThreaded' in `SingleThreadedSchedulerClient()`) - that callbacks pushed to the `SingleThreadedSchedulerClient()` obey the single threaded model for memory and execution - specifically, the callbacks are executed fully and in order, and even in cases where a subsequent callback is executed by a different thread, sequential consistency of memory for all threads executing these callbacks is maintained.
Maintaining memory consistency should make the api more developer friendly - especially for users of the validationinterface. To the extent that there are performance implications from this decision, these are not currently present in practice because all use of this scheduler happens on a single thread currently, furthermore the lock should guarantee consistency across callback executions even when callbacks are executed by multiple threads (as the test does).
Tree-SHA512: 5d95a7682c402e5ad76b05bc9dfbca99ca64105f62ab9e78f6fc0f6ea8c5277aa399fbb94298e35cc677b0c2181ff17259584bb7ae230e38aa68b85ecbc22856
Note that the CScheduler thread cant be running at this point,
it has already been stopped with the rest of the init threadgroup.
Thus, just calling any remaining loose callbacks during Shutdown()
is sane.
This will be used by CValidationInterface soon.
This requires a bit of work as we need to ensure that most of our
callbacks happen in-order (to avoid synchronization issues in
wallet) - we keep our own internal queue and push things onto it,
scheduling a queue-draining function immediately upon new
callbacks.
On a busy or slow system, the CScheduler unit test could fail because it
assumed all threads would be done after a couple of milliseconds.
Replace the hard-coded sleep with CScheduler stop() method that
will cleanly exit the servicing threads when all tasks are completely
finished.
