Hi Ben,
first, thanks for responding dispassionately to the technical issues.
As far as thread-safety I thought the issue with the transcript was not
providing some form of protection against unpredictable interleavings of output
from multiple separate processes, but was just avoiding lock-up. If one
outputs to another kind of stream (file, terminal window) from multiple
processes you typically get jumbled output on a first-come first-served basis.
What one wants IMO is that the transcript remains robust, with no red morphs of
death, not that output is interleaved with a specific policy.
Eliot (phone)
On May 9, 2015, at 8:54 AM, Ben Coman <[email protected]> wrote:
>
>
> On Sat, May 9, 2015 at 10:35 PM, Eliot Miranda <[email protected]>
> wrote:
>>
>>
>> On Sat, May 9, 2015 at 7:09 AM, Ben Coman <[email protected]> wrote:
>>> From my limited experience bug hunting, calling #changed: from a thread
>>> other than the UI thread is a source of evil. There are too many
>>> assumptions throughout the system that the UI is single threaded. Can
>>> anyone advise me that is not a proper belief?
>>>
>>> Then that implies that a Transcript implementation where #nextPut: direct
>>> calls #changed:
>>> is not appropriate for use with multi-threaded applications. In Pharo,
>>> #changed: is only called from #stepGlobal, which is called from
>>> doOneCycle:. (This came about as a last minute bug fix before Pharo 3
>>> release and maybe could use some cleanup.
>>>
>>> Separating the UI from Transcript into its own viewer might be a good idea,
>>> but actually it would not solve Stef's case since his code would still be
>>> running in the UI thread -- unless the viewer ran in another thread, which
>>> would have its own complexities.
>>>
>>> I think the point about efficiency is significant. The following example...
>>> Time millisecondsToRun: [ 1000 timesRepeat: [ Transcript show: 'x' ] ]
>>> on Squeak 4.5 --> 12749ms
>>> on Pharo 50029 --> 2ms
>>>
>>> This better performance helped me a lot trying to understand the high
>>> priority timerEventLoop being able to indiscriminately scatter Transcript
>>> tracing through that code. I believe its also probably beneficial for
>>> working with externally triggered semaphores and timing sensitive race
>>> conditions.
>>>
>>> So we have two mutually exclusive cases:
>>> * better interactivity, poorer system performance
>>> * faster system performance, worse interactivity
>>>
>>> Which of these is broken depends on your viewpoint.
>>
>> Something that runs fast but is incorrect is still incorrect. The fact that
>> the transcript doesn't output until a world step is possible is a bug. It
>> forces programs that use the transcript to be rewritten in order to see
>> transcript output.
>
> As a point of comparison for correctness, for the following...
>
> Transcript clear.
> [ $a asciiValue to: $z asciiValue do: [ :c |
> [ 1 to: 9 do: [ :i | Transcript show: c asCharacter printString , i
> printString , ' ' ] ] forkAt: 40
> ].
> ] forkAt: 41
>
> Squeak 4.5 gives...
> $a1 $a2 $a3 $a4 $a5 $a6 $a7 $a8 $a9 $b1 $b2 $b3 $b4 $b5 $b5 $c1 $c2 $c3 $c4
> $c5 $c6 $c7 $c8 $c9 $d1 $d2 $d3 $d4 $d5 $d6 $d7 $d8 $d9 $d9 $e2 $g2 $h2 $h2
> $i2 $k2 $k2 $l2 $n2 $n2 $o2 $o2 $r2 $s2 $t2 $u2 $u2 $v2 $x2 $y2 $z2 $z2 $b7
> $f3 $e3 $e3 $g3 $j3 $h3 $i3 $k3 $k3 $m3 $n3 $p3 $p3 $q3 $o3 $s3 $t3 $t3 $u3
> $v3 $x3 $y3 $z3 $b8 $f4 $e4 $e4 $g4 $h4 $i4 $k4 $l4 $m4 $m4 $n4 $r4 $q4 $o4
> $o4 $s4 $w4 $u4 $u4 $v4 $y4 $y4 $z4 $z4 $f5 $j5 $j5 $g5 $i5 $k5 $l5 $l5 $m5
> $m5 $n5 $q5 $o5 $s5 $s5 $t5 $u5 $u5 $x5 $y5 $z5 $f6 $f6 $h6 $h6 $g6 $g6 $k6
> $p6 $m6 $r6 $r6 $n6 $o6 $s6 $s6 $w6 $u6 $x6 $x6 $e7 $f7 $j7 $h7 $h7 $i7 $l7
> $l7 $k7 $m7 $m7 $q7 $n7 $n7 $o7 $t7 $w7 $w7 $u7 $v7 $x7 $z7 $z7 $e8 $e8 $h8
> $g8 $i8 $i8 $l8 $k8 $k8 $m8 $q8 $n8 $n8 $s8 $t8 $w8 $y8 $y8 $u8 $x8 $z8 $f9
> $f9 $e9 $h9 $h9 $g9 $p9 $p9 $k9 $r9 $r9 $m9 $n9 $n9 $o9 $t9 $t9 $w9 $v9 $u9
> $u9 $z9 $x9
>
> Pharo 50041 gives...
> $a1 $a2 $a3 $a4 $a5 $a6 $a7 $a8 $a9 $b1 $b2 $b3 $b4 $b5 $b6 $b7 $b8 $b9 $c1
> $c2 $c3 $c4 $c5 $c6 $c7 $c8 $c9 $d1 $d2 $d3 $d4 $d5 $d6 $d7 $d8 $d9 $e1 $e2
> $e3 $e4 $e5 $e6 $e7 $e8 $e9 $f1 $f2 $f3 $f4 $f5 $f6 $f7 $f8 $f9 $g1 $g2 $g3
> $g4 $g5 $g6 $g7 $g8 $g9 $h1 $h2 $h3 $h4 $h5 $h6 $h7 $h8 $h9 $i1 $i2 $i3 $i4
> $i5 $i6 $i7 $i8 $i9 $j1 $j2 $j3 $j4 $j5 $j6 $j7 $j8 $j9 $k1 $k2 $k3 $k4 $k5
> $k6 $k7 $k8 $k9 $l1 $l2 $l3 $l4 $l5 $l6 $l7 $l8 $l9 $m1 $m2 $m3 $m4 $m5 $m6
> $m7 $m8 $m9 $n1 $n2 $n3 $n4 $n5 $n6 $n7 $n8 $n9 $o1 $o2 $o3 $o4 $o5 $o6 $o7
> $o8 $o9 $p1 $p2 $p3 $p4 $p5 $p6 $p7 $p8 $p9 $q1 $q2 $q3 $q4 $q5 $q6 $q7 $q8
> $q9 $r1 $r2 $r3 $r4 $r5 $r6 $r7 $r8 $r9 $s1 $s2 $s3 $s4 $s5 $s6 $s7 $s8 $s9
> $t1 $t2 $t3 $t4 $t5 $t6 $t7 $t8 $t9 $u1 $u2 $u3 $u4 $u5 $u6 $u7 $u8 $u9 $v1
> $v2 $v3 $v4 $v5 $v6 $v7 $v8 $v9 $w1 $w2 $w3 $w4 $w5 $w6 $w7 $w8 $w9 $x1 $x2
> $x3 $x4 $x5 $x6 $x7 $x8 $x9 $y1 $y2 $y3 $y4 $y5 $y6 $y7 $y8 $y9 $z1 $z2 $z3
> $z4 $z5 $z6 $z7 $z8 $z9
>
> (start your comparison at $b5)
>
> So in one axis Pharo has improved Transcript, but we didn't notice the
> significance of the use case we lost.
>
> cheers -ben
