https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=27b24069d16623ac21e858d998bbaf008c3f0924
commit 27b24069d16623ac21e858d998bbaf008c3f0924 Author: Corinna Vinschen <[email protected]> Date: Tue Sep 7 12:56:48 2021 +0200 Cygwin: pipes: drop "tiny pipe" handling Given we return 1 already if WriteQuotaAvailable is > 0, the condition for tiny pipes is never true. Fix the comments. Signed-off-by: Corinna Vinschen <[email protected]> Diff: --- winsup/cygwin/select.cc | 22 +++++++--------------- 1 file changed, 7 insertions(+), 15 deletions(-) diff --git a/winsup/cygwin/select.cc b/winsup/cygwin/select.cc index ac2fd227e..5e338e43f 100644 --- a/winsup/cygwin/select.cc +++ b/winsup/cygwin/select.cc @@ -608,10 +608,12 @@ pipe_data_available (int fd, fhandler_base *fh, HANDLE h, bool 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(). */ + /* WriteQuotaAvailable is decremented by the number of bytes requested + by a blocking reader on the other side of the pipe. Cygwin readers + are serialized and never request a number of bytes equivalent to the + full buffer size. So WriteQuotaAvailable is 0 only if either the + read buffer on the other side is really full, or if we have non-Cygwin + readers. */ if (fpli.WriteQuotaAvailable > 0) { paranoid_printf ("fd %d, %s, write: size %u, avail %u", fd, @@ -619,17 +621,7 @@ pipe_data_available (int fd, fhandler_base *fh, HANDLE h, bool writing) 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; - } + /* TODO: Buffer really full or non-Cygwin reader? */ } else if (fpli.ReadDataAvailable) {
