https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=00cbbaa33e7183a6b414cc0f36bc6cbf0b22d8ce
commit 00cbbaa33e7183a6b414cc0f36bc6cbf0b22d8ce Author: Takashi Yano <[email protected]> Date: Wed Sep 15 09:55:57 2021 +0900 Cygwin: pipe: Do not call PeekNamedPipe() if it is not necessary. - In pipe_data_available() in select.cc, PeekNamedPipe() call is not needed if WriteQuotaAvailable is non-zero because we already know the write pipe has a space. Therefore, with this patch, PeekNamedPipe() is called only when WriteQuotaAvailable is zero. This makes select() on pipe faster a bit. Diff: --- winsup/cygwin/select.cc | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) diff --git a/winsup/cygwin/select.cc b/winsup/cygwin/select.cc index ac2f3a9e0..fd2312298 100644 --- a/winsup/cygwin/select.cc +++ b/winsup/cygwin/select.cc @@ -633,17 +633,15 @@ pipe_data_available (int fd, fhandler_base *fh, HANDLE h, bool writing) /* Note: Do not use NtQueryInformationFile() for query_hdl because NtQueryInformationFile() seems to interfere with reading pipes in non-cygwin apps. Instead, use PeekNamedPipe() here. */ - if (fh->get_device () == FH_PIPEW) + if (fh->get_device () == FH_PIPEW && fpli.WriteQuotaAvailable == 0) { HANDLE query_hdl = ((fhandler_pipe *) fh)->get_query_handle (); - if (query_hdl) - { - DWORD nbytes_in_pipe; - PeekNamedPipe (query_hdl, NULL, 0, NULL, &nbytes_in_pipe, NULL); - fpli.WriteQuotaAvailable = fpli.InboundQuota - nbytes_in_pipe; - } - else + if (!query_hdl) + return 1; /* We cannot know actual write pipe space. */ + DWORD nbytes_in_pipe; + if (!PeekNamedPipe (query_hdl, NULL, 0, NULL, &nbytes_in_pipe, NULL)) return 1; + fpli.WriteQuotaAvailable = fpli.InboundQuota - nbytes_in_pipe; } if (fpli.WriteQuotaAvailable > 0) {
