Don't make RemoteFileUtils.makeDirectories syncronized

[dongja3]

In what version(s) of Spring Integration are you seeing this issue?
5.3.1.RELEASE

Describe the bug
It caused by org.springframework.integration.file.remote.RemoteFileUtils#makeDirectories, which is synchronized static method, when there are lots of (S)ftp move operation concurrently and slow speed of network, all requests of AbstractRemoteFileOutboundGateway#mv are queued and observed as very slow speed.

https://stackoverflow.com/questions/62772002/outbound-gateway-executes-the-mv-command-very-slowly

Expected behavior
in api doc, RemoteFileUtils#makeDirectories is static not synchronized,
https://docs.spring.io/spring-integration/docs/5.3.1.RELEASE/api/
However, in source code is static and syncronized.

[garyrussell]

It was synchronized to fix a race condition.

#2915

[artembilan]

I think the request is valid. Even with that synchronized we definitely still may fail with race condition when our application is in cluster, so different nodes may try to create the same dirs at the same moment.

It is better to rework this logic to really catch an exception from the session.mkdir(path) when it says that Eine Datei kann nicht erstellt werden, wenn sie bereits vorhanden ist (A file cannot be created if it already exists). Probably as a second session.exists(path) check in the catch block...

WDYT?

[garyrussell]

Agreed; yes.

[dongja3]

Hi, Aterm, Gary
thanks for your prompt feedback, and look forward to the new release.