The offending function in my case seems to be peek-bytes-avail!
The busy wait is entered on line 284 of collects/file/gunzip.rkt. Here's
what happens when I add some tracing to gunzip.rkt and then try to
inflate a Racket pipe:
...
+ (displayln "before read-bytes!")
(read-bytes! buffer input-port 0 (max 0 (- buf-max MAX-LOOKAHEAD)))
+ (displayln "after read-bytes!")
;; Even though we won't actually use bytes that we "unwind",
;; setting `buf-pos' to the number of unwound bytes lets us
;; keep track of how much to not actually read at the end.
(set! buf-pos (min MAX-LOOKAHEAD buf-max)))
;; Peek (not read) some available bytes:
+ (displayln "before peek-bytes-avail!")
(let ([got (peek-bytes-avail! buffer buf-pos #f input-port buf-pos
BUFFER-SIZE)])
+ (displayln "after peek-bytes-avail!")
...
+ (trace READBITS)
Output:
...
>(READBITS 9)
<#<void>
>(READBITS 9)
before read-bytes!
after read-bytes!
before peek-bytes-avail!
That's it. Racket is busy-waiting in peek-bytes-avail!
On Wed, Sep 03, 2014 at 10:52:18PM +0200, Jan Dvořák wrote:
> Hello,
>
> I am hitting a rather uncomfortable bug that causes runtime to start
> internal busy-waiting at around:
>
> #0 scheme_block_until(_f=<syncing_ready>,
> fdf=<scheme_syncing_needs_wakeup>)
> at ../src/thread.c:5199
> #1 do_sync (name="sync", with_break=0, with_timeout=0)
> at ../src/thread.c:7109
>
> It goes through ../src/thread.c:5190, which Matthew mentions in one of his
> recent patches.
>
> The code that manages to trigger this have been written under NDA and cannot
> be published. I have not yet managed to reproduce the issue separately, but
> it seems that this might not be the only instance:
>
> (09:28:36 PM) m4burns: Mordae: I'm having a similar problem somewhere in
> `inflate`. Haven't applied a debugger yet, but
> there's certainly no busy waiting in the script.
>
> I am stuck and would like to ask for your help.
>
> Best regards,
> Jan Dvorak
>
>
>
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