Fiber channel close mode

Option: fiber_channel_close_mode

Before the change, there was an unexpected behavior when using channel:close() because it closed the channel entirely and discarded all unread events.

The compat module allows you chose between the channel force and graceful closing. The latter is a new behavior.

 
tarantool> compat = require('compat')---...tarantool> compat---- - yaml_pretty_multiline: default (old)  - json_escape_forward_slash: default (old)  - fiber_channel_close_mode: default (old)...tarantool> fiber = require('fiber')---...tarantool> ch = fiber.channel(10)---...tarantool> ch:put('one')---- true...tarantool> ch:put('two')---- true...tarantool> ch:get()---- one...tarantool> ch:close()---...tarantool> ch:get()---- null...tarantool> compat.fiber_channel_close_mode = 'new'---...tarantool> ch = fiber.channel(10)---...tarantool> ch:put('one')---- true...tarantool> ch:put('two')---- true...tarantool> ch:get()---- one...tarantool> ch:close()---...tarantool> ch:get()---- two...tarantool> ch:get()---- null...

You can select new/old behavior in compat. It will affect all existing channels and the future ones.

At this point, no incompatible modules are known.

The new behavior is mostly backward compatible. The only known problem that can appear is when the code relies on channel being entirely closed after ch:close() and ch:get() returning nil.