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Cygwin: pipe_data_available: cleanup code

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* Don't use a bool var to store three states (-1, 0, 1).
* Correctly check for NT_SUCCESS of a function returning NTSTATUS.
* Straighten out code for better readability.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This commit is contained in:
Corinna Vinschen 2017-11-15 20:11:05 +01:00
parent 0f88d21e4d
commit 57732f9b4b
1 changed files with 40 additions and 27 deletions
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67
winsup/cygwin/select.cc
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@ -568,45 +568,58 @@ pipe_data_available (int fd, fhandler_base *fh, HANDLE h, bool writing)
{
IO_STATUS_BLOCK iosb = {{0}, 0};
FILE_PIPE_LOCAL_INFORMATION fpli = {0};
NTSTATUS status;
bool res;
if (fh->has_ongoing_io ())
res = false;
else if (NtQueryInformationFile (h, &iosb, &fpli, sizeof (fpli),
FilePipeLocalInformation))
return 0;
status = NtQueryInformationFile (h, &iosb, &fpli, sizeof (fpli),
FilePipeLocalInformation);
if (!NT_SUCCESS (status))
{
/* If NtQueryInformationFile fails, optimistically assume the
pipe is writable. This could happen if we somehow
inherit a pipe that doesn't permit FILE_READ_ATTRIBUTES
access on the write end. */
select_printf ("fd %d, %s, NtQueryInformationFile failed",
fd, fh->get_name ());
res = writing ? true : -1;
select_printf ("fd %d, %s, NtQueryInformationFile failed, status %y",
fd, fh->get_name (), status);
return writing ? 1 : -1;
}
else if (!writing)
if (writing)
{
/* If there is anything available in the pipe buffer then signal
that. This means that a pipe could still block since you could
be trying to write more to the pipe than is available in the
buffer but that is the hazard of select(). */
fpli.WriteQuotaAvailable = fpli.OutboundQuota - fpli.ReadDataAvailable;
if (fpli.WriteQuotaAvailable > 0)
{
paranoid_printf ("fd %d, %s, write: size %u, avail %u", fd,
fh->get_name (), fpli.OutboundQuota,
fpli.WriteQuotaAvailable);
return 1;
}
/* If we somehow inherit a tiny pipe (size < PIPE_BUF), then consider
the pipe writable only if it is completely empty, to minimize the
probability that a subsequent write will block. */
if (fpli.OutboundQuota < PIPE_BUF
&& fpli.WriteQuotaAvailable == fpli.OutboundQuota)
{
select_printf ("fd, %s, write tiny pipe: size %u, avail %u",
fd, fh->get_name (), fpli.OutboundQuota,
fpli.WriteQuotaAvailable);
return 1;
}
}
else if (fpli.ReadDataAvailable)
{
paranoid_printf ("fd %d, %s, read avail %u", fd, fh->get_name (),
fpli.ReadDataAvailable);
res = !!fpli.ReadDataAvailable;
return 1;
}
else if ((res = (fpli.WriteQuotaAvailable = (fpli.OutboundQuota -
fpli.ReadDataAvailable))))
/* If there is anything available in the pipe buffer then signal
that. This means that a pipe could still block since you could
be trying to write more to the pipe than is available in the
buffer but that is the hazard of select(). */
paranoid_printf ("fd %d, %s, write: size %u, avail %u", fd,
fh->get_name (), fpli.OutboundQuota,
fpli.WriteQuotaAvailable);
else if ((res = (fpli.OutboundQuota < PIPE_BUF &&
fpli.WriteQuotaAvailable == fpli.OutboundQuota)))
/* If we somehow inherit a tiny pipe (size < PIPE_BUF), then consider
the pipe writable only if it is completely empty, to minimize the
probability that a subsequent write will block. */
select_printf ("fd, %s, write tiny pipe: size %u, avail %u",
fd, fh->get_name (), fpli.OutboundQuota,
fpli.WriteQuotaAvailable);
return res ?: -!!(fpli.NamedPipeState & FILE_PIPE_CLOSING_STATE);
if (fpli.NamedPipeState & FILE_PIPE_CLOSING_STATE)
return -1;
return 0;
}
static int