C++ TSocket default linger setting breaks forked parent process
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Key: THRIFT-748
URL: https://issues.apache.org/jira/browse/THRIFT-748
Project: Thrift
Issue Type: Bug
Components: Library (C++)
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
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.
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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