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README.md

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What is this?

This repository contains a testcase for opening pipes for reading and writting multiples times in Cygwin.

The testcase is available in both Python and C++. Use whichever you're comfortable with.

Instructions:

git clone https://github.com/joaoe/cygwin-pipe-testcase.git
cd cygwin-pipe-testcase
./run-all

Behavior

Current behavior on Cygwin:

0. open(r) = /tmp/cyg_pipe_test -> 8
0. poll    = <empty>
0. read    = errno ECOMM(70): Communication error on send
1. open(w) = /tmp/cyg_pipe_test -> 9
1. poll    = 8: POLLIN(0x1)
1. read    = b'test 1'
2. poll    = 8: POLLIN(0x1)|POLLPRI(0x2)
2. read    = b''
3. open(w) = /tmp/cyg_pipe_test -> errno ENXIO(6): No such device or address
3. poll    = 8: POLLIN(0x1)|POLLPRI(0x2)
3. read    = b''
4. poll    = 8: POLLIN(0x1)|POLLPRI(0x2)
4. read    = b''
FAIL: got 5 errors

Expected behavior on Linux (ignore the difference in file descriptor values):

0. open(r) = /tmp/cyg_pipe_test -> 3
0. poll    = <empty>
0. read    = b''
1. open(w) = /tmp/cyg_pipe_test -> 4
1. poll    = 3: POLLIN(0x1)
1. read    = b'test 1'
2. poll    = 3: POLLHUP(0x10)
2. read    = b''
3. open(w) = /tmp/cyg_pipe_test -> 4
3. poll    = 3: POLLIN(0x1)
3. read    = b'test 2'
4. poll    = 3: POLLHUP(0x10)
4. read    = b''
PASS

Conclusions:

  • read() on a non-blocking pipe opened for reading without a connected writer returns the error ECOMM, while it should just return a read of size 0.
  • the pipe is opened in write and non-blocking mode
  • poll() on the read FD sets POLLPRI which is behavior not specified in the posix specification for pipes.
  • the file descriptor for writting is closed, the read descriptor is left open
  • poll() will continue to report POLLIN|POLLPRI after the writer has disconnected, instead of reporting POLLHUP. POLLHUP, POLLERR and POLLNVAL can be returned even though they have not been requested when calling poll(). POLLHUP means that the writer has closed the pipe.
  • a second open() of the pipe in write and non-blocking mode fails with the error ENXIO, instead of returning a new valid file descriptor. The same attempt but opening in blocking mode just blocks the open() indefinitely. The ENXIO error should be reported when opening a pipe in non-blocking and write mode while there is not a reader connected.