From 34b14470406cb9551f98707bf63175811a506523 Mon Sep 17 00:00:00 2001 From: Corinna Vinschen Date: Wed, 15 Sep 2021 14:17:59 +0200 Subject: [PATCH] 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 --- 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; -- 2.43.5