Re: Support to define custom wait events for extensions

Hi,

Thanks for your comments about the v2 patches. I updated to v3 patches.

The main changes are:
* remove the AddinShmemInitLock assertion
* add the new lock (WaitEventExtensionLock) to wait_event_names.txt
* change "static const int wee_hash_XXX_size" to "#define XXX"
* simplify worker_spi. I removed codes related to share memory and
   try to allocate the new wait event before waiting per background 
worker.
* change to elog from ereport because the errors are for developers.
* revise comments as advised.
* fix the request size for shared memory correctly
* simplify dblink.c
* fix process ordering of WaitEventExtensionNew() as advised to
   avoid leading illegal state.

In addition, I change the followings:
* update about custom wait events in sgml. we don't need to use
   shmem_startup_hook.
* change the hash names for readability.
  (ex. WaitEventExtensionNameHash -> WaitEventExtensionHashById)
* fix a bug to fail to get already defined events by names
   because HASH_BLOBS was specified. HASH_STRINGS is right since
   the key is C strings.

I create a new entry in commitfest for CI testing.
(https://commitfest.postgresql.org/44/4494/)

Thanks for closing the former entry.
(https://commitfest.postgresql.org/43/4368/)

Regards,
-- 
Masahiro Ikeda
NTT DATA CORPORATION