diff options
Diffstat (limited to 'winsup/cygwin/select.cc')
| -rw-r--r-- | winsup/cygwin/select.cc | 67 |
1 files changed, 40 insertions, 27 deletions
diff --git a/winsup/cygwin/select.cc b/winsup/cygwin/select.cc index f5a9938..0cd2dc9 100644 --- a/winsup/cygwin/select.cc +++ b/winsup/cygwin/select.cc @@ -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; + } + 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 (!writing) + 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 |