Really slow named pipes

Duane Clark dclark at
Sun Aug 24 13:15:52 CDT 2003

Duane Clark wrote:
> This is a bit old, from May, but anyhow...
> The patch to implement anonymous pipes on top of named pipes:
> along with a corresponding bug fix:
> causes Xilinx ISE to run really, really slow.
> It has a window to which messages are sent via a pipe, and what I see 
> now is that one line comes out every 2/3 of a second or so, as regular 
> as a clock at least by eye. I can revert those two patches, and it goes 
> back to spitting out the messages very fast. Since there are a lot of 
> messages being sent, the current version slows the app down to a crawl.

A bit more info about what is happening, as best as I can tell. It looks 
like the message window is doing a PeekNamedPipe about every 2/3 of a 
second; hence the timing that I am seeing.

So the problem appears to be that in the new implementation, the write 
to the pipe is being blocked on every call, until a read has happened. 
What should be happening is that the write should only block if the pipe 
is full. Does that help someone know where to look?

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