Fix executable dictionary source hang

[alexey-milovidov]

Changelog category (leave one):

• Bug Fix

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):
Fix executable dictionary source hang. In previous versions, when using some formats (e.g. JSONEachRow) data was not feed to a child process before it outputs at least something. This closes #1697. This closes #2455.

[nikitamikhaylov]

I've read the code of ExecutableDictionarySource and everything near with it. Why do you think that BOM caused deadlock? I think it is because of std::packaged_task which is executed asynchronously (by itself, but we call it from another thread for unknown reason). So, we called operator() here, but according to notes here it is synchronized only with calling of get() on its std::future. I think it means that we can't guarantee whether or not the function is executed after the operator() is called. It seems that in our case the underlying function wasn't executed. The author wrote in the issue, that ClickHouse writes to stdin only after the process writes something to stdout, and this behavior is explained by reasoning above.

[nikitamikhaylov]

I think in JSON we don't have comments.

Suggested change

	"01474_executable_dictionary" /// informational stderr from sanitizer at start
	"01474_executable_dictionary"

[alexey-milovidov]

We do.

[alexey-milovidov]

Integration test:
test_adaptive_granularity/test.py::test_version_update_two_nodes

• flaky test @alesapin

[alexey-milovidov]

AST Fuzzer: #14677