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tst_QProcess::startStopStartStopBuffers: depend less on OS configuration

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The comment in this function made it clear that it really depended on
the size of the pipe buffer in the OS. I don't see a way to make a pipe
default to a different size on Linux -- it always defaults to
PIPE_DEF_BUFFERS (16) and that value is only increased as a result of
fcntl(F_SETPIPE_SZ), which we don't do. But we can be defensive and
simply write until the OS can't take any more data.

Drive-by update the comment on Windows to be clear that bytesToWrite()
does work, but only while the child process is still running.

Pick-to: 6.6
Task-number: QTBUG-80953
Change-Id: I9d43e5b91eb142d6945cfffd17866d22a4127e5e
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
This commit is contained in:
Thiago Macieira 2023-09-19 15:25:05 -07:00
parent 5a2aa12147
commit a3f2ddc230
1 changed files with 13 additions and 8 deletions
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21
tests/auto/corelib/io/qprocess/tst_qprocess.cpp
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@ -2889,14 +2889,18 @@ void tst_QProcess::startStopStartStopBuffers()
}
// We want to test that the write buffer still has bytes after the child
// exiting. We do that by writing to a child process that never reads. We
// just have to write more data than a pipe can hold, so that even if
// QProcess finds the pipe writable (during waitForFinished() or in the
// QWindowsPipeWriter thread), some data will remain. The worst case I know
// of is Linux, which defaults to 64 kB of buffer.
// exits. We can do that by writing data until the OS stops consuming data,
// indicating that the pipe buffers are full. The initial value of 128 kB
// should make this loop typicall run only once; the worst case I know of
// is Linux, which defaults to 64 kB of buffer.
process.write(QByteArray(128 * 1024, 'a'));
QVERIFY(process.bytesToWrite() > 0);
QByteArray chunk(128 * 1024, 'a');
do {
process.write(chunk);
QVERIFY(process.bytesToWrite() > 0);
process.waitForBytesWritten(1);
} while (process.bytesToWrite() == 0);
chunk = {};
process.kill();
QVERIFY(process.waitForFinished());
@ -2904,7 +2908,8 @@ void tst_QProcess::startStopStartStopBuffers()
#ifndef Q_OS_WIN
// confirm that our buffers are still full
// Note: this doesn't work on Windows because our buffers are drained into
// QWindowsPipeWriter before being sent to the child process.
// QWindowsPipeWriter before being sent to the child process and are lost
// in waitForFinished() -> processFinished() -> cleanup().
QVERIFY(process.bytesToWrite() > 0);
QVERIFY(process.bytesAvailable() > 0); // channelMode1 is not ForwardedChannels
if (channelMode1 == QProcess::SeparateChannels || channelMode1 == QProcess::ForwardedOutputChannel) {