Upgraded address stops working after all references are dropped

[fuchsnj]

If you upgrade an Address to a SyncAddress, then drop the SyncAddress, then upgrade the address again, the SyncAddress returned during the 2nd upgrade does not work.

I was able to create a minimal example showing this bug
https://github.com/fuchsnj/actix_bug/blob/master/src/main.rs

The example program upgrades an address twice, each time sending a message that should be printed. It should print "Handling message!" twice, but it's only printing once.

I believe this is because when the last reference to SyncAddress is dropped, the underlying sender is closed. If you upgrade an address after this, it re-uses the tx/rx from the first one that was already closed.

In my example code, you can uncomment one of the lines which prevents the SyncAddress from being dropped, and the bug goes away.

Also, if you comment out the line in actix that closes this sender, the bug also goes away.
https://github.com/actix/actix/blob/master/src/queue/sync.rs#L763

[fafhrd91]

Very nice!

Would you provide PR?

[fuchsnj]

I'll open a PR for this one. Still need to get more familiar with the code to figure out the best way to solve this one. If you have any ideas that would be helpful.

[fafhrd91]

I am traveling at the moment, won’t be able to help next 10 hours

[fafhrd91]

this is actually tricky problem, let me fix it

[fafhrd91]

fixed in master