Just for fun, I implemented a toy background worker tonight using the new bgworker framework. Generally, it went well, and I'm pleased with the design of the new facility. However, I did notice one oddity. I initialized the worker flags like this:
worker.bgw_flags = BGWORKER_SHMEM_ACCESS;
And... latches didn't work. It turns out that if you request database access, then the SIGUSR1 handler is set to procsignal_sigusr1_handler, which is fine. But if you don't, it gets set to SIG_IGN. And the result of *that* is that if someone sets a latch for which the background process is waiting, the background process fails to notice.
Now, once you understand what's going on here, it's not hard to work around. But it seems to me that it would be a saner default to set the signal handler to something like the bgwriter handler, which just calls latch_sigusr1_handler.
You can have a try with the example I provided, then try to reload parameters with "pg_ctl reload" and you will notice that bgworkers do not process SIGHUP as a normal backend would do. -- Michael
