[M3devel] Fwd: Strange code in Rd.CharsReady

[Mika Nystrom]

not sure the list allows my other email address to email to it...

---------- Forwarded message ----------
From: Mika Nystrom <mika at alum.mit.edu>
Date: Sun, Dec 10, 2017 at 1:07 PM
Subject: Strange code in Rd.CharsReady
To: m3devel at elegosoft.com


Hello m3devel,

Long time no see!

I am trying to resurrect some old code I have, and I have run into a
strange issue.

According to

https://github.com/modula3/cm3/blame/master/m3-libs/libm3/src/rw/Rd.m3

the current source code for the routine Rd.CharsReady is as follows below.

I am truly suspicious of line 389, which says it comes from some Unicode
merge.

IF NextBuff (rd) THEN RETURN 1 END (*line 389*)

I have a program that misbehaves.

This program appears to be BLOCKING in CharsReady.  This behavior obviously
defeats the purpose of CharsReady.  I can't seem to cut and paste the
traceback for some reason but it's calling Rd__NextBuff at line 151 and
further then to ConnRW__RdSeek  with dontBlock FALSE (so "OK to block") and
then SchedulerPosix__AlertWait.

The old version of line 389 I believe was

IF rd.seek(rd.cur, TRUE) = SeekResult.Eof THEN RETURN 1 END

where TRUE means "don't block".

Can someone tell me the rationale for the change and whether I am correct
if I say that the new version is wrong?

I am wonder how this change could even have gotten into the code in the
first place if it's causing CharsReady to block, seems like a pretty
obvious bug and I don't see a reason for tthe change in the first place.

Mika



PROCEDURE CharsReady(rd: T): CARDINAL
383
RAISES {Failure} =
[image: @hosking] <https://github.com/hosking>
Hide warning.
<https://github.com/modula3/cm3/commit/dbbcc11269c5aa10a13a61572e67a78cb03a7030>
3 years ago
<https://github.com/modula3/cm3/blame/7032bc21f3fa31450a6600b61de7f0523516309f/m3-libs/libm3/src/rw/Rd.m3>
384
<*FATAL Thread.Alerted*>
[image: @jaykrell] <https://github.com/jaykrell>
initial diff from ../config/PPC_LINUX
<https://github.com/modula3/cm3/commit/2412437e3043bdfcb5f13463b5b445c78aeb4c9b>
10 years ago
385
BEGIN
[image: @RodneyBates] <https://github.com/RodneyBates>
Merge Unicode branch into head. For a summary of the changes, see
<https://github.com/modula3/cm3/commit/ea494d1b46c34a6c4c805322cfe6b1c02bfb2bf0>
4 years ago
<https://github.com/modula3/cm3/blame/e5a6e4ae7feabce4e375a1445ea28dc66a174d58/m3-libs/libm3/src/rw/Rd.m3>
386
LOCK rd DO
[image: @jaykrell] <https://github.com/jaykrell>
initial diff from ../config/PPC_LINUX
<https://github.com/modula3/cm3/commit/2412437e3043bdfcb5f13463b5b445c78aeb4c9b>
10 years ago
387
IF rd.cur = rd.hi THEN
388
IF rd.closed THEN Die() END;
[image: @RodneyBates] <https://github.com/RodneyBates>
Merge Unicode branch into head. For a summary of the changes, see
<https://github.com/modula3/cm3/commit/ea494d1b46c34a6c4c805322cfe6b1c02bfb2bf0>
4 years ago
<https://github.com/modula3/cm3/blame/e5a6e4ae7feabce4e375a1445ea28dc66a174d58/m3-libs/libm3/src/rw/Rd.m3>
389
IF NextBuff (rd) THEN RETURN 1 END
[image: @jaykrell] <https://github.com/jaykrell>
initial diff from ../config/PPC_LINUX
<https://github.com/modula3/cm3/commit/2412437e3043bdfcb5f13463b5b445c78aeb4c9b>
10 years ago
390
END;
391
RETURN rd.hi - rd.cur;
[image: @RodneyBates] <https://github.com/RodneyBates>
Merge Unicode branch into head. For a summary of the changes, see
<https://github.com/modula3/cm3/commit/ea494d1b46c34a6c4c805322cfe6b1c02bfb2bf0>
4 years ago
<https://github.com/modula3/cm3/blame/e5a6e4ae7feabce4e375a1445ea28dc66a174d58/m3-libs/libm3/src/rw/Rd.m3>
392
END;
[image: @jaykrell] <https://github.com/jaykrell>
initial diff from ../config/PPC_LINUX
<https://github.com/modula3/cm3/commit/2412437e3043bdfcb5f13463b5b445c78aeb4c9b>
10 years ago
393
END CharsReady;
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