[jira] [Closed] (THRIFT-748) C++ TSocket default linger setting breaks forked parent process

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

     [ https://issues.apache.org/jira/browse/THRIFT-748?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

James E. King, III closed THRIFT-748.
-------------------------------------
    Resolution: Won't Fix
      Assignee: James E. King, III

In light of the resolution of THRIFT-747, I am resolving this issue the same way. 

> C++ TSocket default linger setting breaks forked parent process
> ---------------------------------------------------------------
>
>                 Key: THRIFT-748
>                 URL: https://issues.apache.org/jira/browse/THRIFT-748
>             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
>            Assignee: James E. King, III
>            Priority: Trivial
>         Attachments: thrift_linger_example.cpp
>
>   Original Estimate: 72h
>  Remaining Estimate: 72h
>
> If a Thrift C++ Client opens a TSocket, writes some data, then calls fork(), the child process can terminate the parent processes' connection by deleting its copy of the parent TSocket.
> In particular,
> the default setting of lingerOn_ = 1 causes a RST to be sent in close(socket_) in TSocket->close() 
> Discussion:
> This behaviour is identical to the behaviour of unix sockets when SO_LINGER is set (implementations vary).
> However, the SO_LINGER default for sockets is off not on. This provides unexpected behaviour in TSocket.
> 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 processes all have to call TSocket->setLinger(0,0) or (1,timeout) before deleting the TSocket, closing the TSocket, or exiting. (This workaround only succeeds with the suggested fix in [#THRIFT-747] ).
> However, the design choice also prevents deadlock/slowdown issues where a forked process holds open a copy of the parent's Thrift connections. It also makes close non-blocking, which is ideal in a destructor.
> 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 default linger interval of 0 turns the linger setting into a hard reset.
> And in the absence of linger, the kernel can usually send small thrift messages by itself.
> Options:
>   * Change the default lingerOn to 0 - rely on the kernel to resend a limited number of times
>   * Change the default lingerVal to > 0
>     - a large value like INT_MAX would match the default connection, send, and recv 'no timeout' behaviour
> TODO:
>   * Confirm issue on Linux - see attached test code
>   * Decide if a change to the defaults is needed
>   * Document workaround after resolution of [#THRIFT-747] - call TSocket->setLinger(0,0) or (1,timeout) if forking



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