1. Thrift
  2. THRIFT-747

C++ TSocket->close calls shutdown breaking forked parent process


    • Type: Bug Bug
    • Status: Open
    • Priority: Minor Minor
    • Resolution: Unresolved
    • Affects Version/s: 0.2, 0.3
    • Fix Version/s: None
    • Component/s: C++ - Library
    • Labels:
    • Environment:

      Cygwin 1.7.1 on Windows XP SP3, Thrift 0.2.0 & r760184 & Trunk


      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_)


      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
      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.


      • 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.


      • 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)
      1. thrift_shutdown_example.cpp
        4 kB
        Tim Wilson-Brown
      2. TSocket-020-fix.cpp
        16 kB
        Tim Wilson-Brown
      3. TSocket-020-fix.h
        5 kB
        Tim Wilson-Brown

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            • Assignee:
              Tim Wilson-Brown
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