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* [newlib-cygwin] Cygwin: pipes: don't call NtQueryInformationFile on read side of pipes
@ 2021-09-15 13:42 Corinna Vinschen
0 siblings, 0 replies; only message in thread
From: Corinna Vinschen @ 2021-09-15 13:42 UTC (permalink / raw)
To: cygwin-cvs
https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=34b14470406cb9551f98707bf63175811a506523
commit 34b14470406cb9551f98707bf63175811a506523
Author: Corinna Vinschen <corinna@vinschen.de>
Date: Wed Sep 15 14:17:59 2021 +0200
Cygwin: pipes: don't call NtQueryInformationFile on read side of pipes
NtQueryInformationFile hangs if it's called on the read side handle of
a pipe while another thread or process is performing a blocking read.
Avoid select potentially hanging by calling NtQueryInformationFile
only on the write side of the pipe and using PeekNamedPipe otherwise.
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
Diff:
---
winsup/cygwin/select.cc | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/winsup/cygwin/select.cc b/winsup/cygwin/select.cc
index a09d8a34d..566cf66d6 100644
--- a/winsup/cygwin/select.cc
+++ b/winsup/cygwin/select.cc
@@ -587,6 +587,14 @@ no_verify (select_record *, fd_set *, fd_set *, fd_set *)
static int
pipe_data_available (int fd, fhandler_base *fh, HANDLE h, bool writing)
{
+ if (fh->get_device () == FH_PIPER)
+ {
+ DWORD nbytes_in_pipe;
+ if (!writing && PeekNamedPipe (h, NULL, 0, NULL, &nbytes_in_pipe, NULL))
+ return nbytes_in_pipe > 0;
+ return -1;
+ }
+
IO_STATUS_BLOCK iosb = {{0}, 0};
FILE_PIPE_LOCAL_INFORMATION fpli = {0};
NTSTATUS status;
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