[jira] [Commented] (THRIFT-747) C++ TSocket->close calls shutdown breaking forked parent process

["James E. King, III (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/THRIFT-747?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14532657#comment-14532657 ] 

James E. King, III commented on THRIFT-747:
-------------------------------------------

Recommend a decision be made by the current maintainers whether to pursue this further or resolve it as won't fix.

> C++ TSocket->close calls shutdown breaking forked parent process
> ----------------------------------------------------------------
>
>                 Key: THRIFT-747
>                 URL: https://issues.apache.org/jira/browse/THRIFT-747
>             Project: Thrift
>          Issue Type: Bug
>          Components: C++ - Library
>    Affects Versions: 0.2, 0.3
>         Environment: Cygwin 1.7.1 on Windows XP SP3, Thrift 0.2.0 & r760184 & Trunk
>            Reporter: Tim Wilson-Brown
>            Priority: Minor
>         Attachments: TSocket-020-fix.cpp, TSocket-020-fix.h, thrift_shutdown_example.cpp
>
>   Original Estimate: 72h
>  Remaining Estimate: 72h
>
> If a Thrift C++ Client opens a TSocket, then calls fork(), the child process can terminate the parent processes' connection by deleting its copy of the parent TSocket.
> In particular,
> TSocket->close() calls shutdown(socket_,SHUT_RDWR) before close(socket_)
> Discussion:
> This behaviour is inconsistent, as it is:
>   * unlike the unix socket close() semantics - close() only affects the process that calls it, and the socket is shut down when all copies of it are closed
>   * unlike the python and java code, which (appears) to only use close()
> This design choice makes it really difficult to program a Thrift client that forks other clients in C++, as the first process to call TSocket->close() terminates all copies of the connection. The child process is unable to cleanup its copy of the parent's connection - this is a particular issue when using shared_ptr because the child process can not even exit().
> However, the design choice also prevents deadlock/slowdown issues where a forked process holds open a copy of the parent's Thrift connections.
> The design choice may also be an attempt to implement the 'block to send then close' behaviour described in http://blog.netherlabs.nl/articles/2009/01/18/the-ultimate-so_linger-page-or-why-is-my-tcp-not-reliable
> However, the shutdown call, and close with the default linger interval of 0 are both hard resets.
> In the absence of linger/shutdown, the kernel can usually send small thrift messages by itself.
> Options:
>   * The most functional resolution would be to implement TSocket->setShutdownOnClose() that allows Thrift users to set their preference for shutdown on socket close or delete. However, this change may also need to be made to other language libraries.
>   * Removing shutdown() from TSocket->close() could break programs that expect TSockets not to stay open if children are still running.
> TODO:
>   * Confirm issue on Linux - see attached test code
>   * Decide how to resolve issue
>   * Create Patch - see attached TSocket.h & TSocket.cpp from Thrift 0.2.0 (I don't know how to generate patches but I'm happy to try and work it out)



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