Details
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Bug
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Status: Closed
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Minor
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Resolution: Won't Fix
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0.2, 0.3
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None
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Cygwin 1.7.1 on Windows XP SP3, Thrift 0.2.0 & r760184 & Trunk
Description
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)
Attachments
Attachments
Issue Links
- blocks
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THRIFT-748 C++ TSocket default linger setting breaks forked parent process
- Closed
- relates to
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THRIFT-5374 SO_LINGER should not be set on AF_UNIX socket on WSL (portability issue)
- Open