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Thread not killable when in 300_000_000.times { |i| var = i } loop #5199

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pitr-ch opened this issue May 27, 2018 · 9 comments
Open

Thread not killable when in 300_000_000.times { |i| var = i } loop #5199

pitr-ch opened this issue May 27, 2018 · 9 comments

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@pitr-ch
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pitr-ch commented May 27, 2018 •
edited

Environment

-> jruby -v
jruby 9.1.17.0 (2.3.3) 2018-04-20 d8b1ff9 Java HotSpot(TM) 64-Bit Server VM 25.71-b01-internal-jvmci-0.42 on 1.8.0_161-b12 +jit [darwin-x86_64]

in a snippet

var     = 0
t = Thread.new do
  300_000_000.times { |i| var = i }
end

Thread.pass while var < 1

p t.status
p Time.now
p t.kill
p t.join
p Time.now

Expected Behavior

the thread is killed immediately

Actual Behavior

however It runs until the loop finishes
@headius
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headius commented May 28, 2018

Not enough checkpointing for thread events in that case, perhaps because there's no calls and no backward branch. I wouldn't consider this representative of any real code, but we should measure the impact of adding a checkpoint to, say, the block exiting.

@subbuss @enebo Thoughts on this one?

@pitr-ch
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pitr-ch commented May 28, 2018 •
edited

Personally I think it should not be possible to write a code in Ruby which would be un-killable. I originally found out by not being able to terminate https://github.com/ruby-concurrency/concurrent-ruby/blob/master/spec/concurrent/synchronization_spec.rb#L15-L20 which less minimal.

@subbuss
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subbuss commented May 28, 2018

@headius, There is a back-edge ... except it is in the jruby library code. That indicates that the library code is missing the checkpoint maybe?

@enebo
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enebo commented May 28, 2018

Shouldn't the times have a threadpoll instr right before jump? (Not convenient for me to check right now).

@headius
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headius commented May 30, 2018

@enebo It would if it were implemented in Ruby. In Java we have to manually add polling to backedges.

@headius
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headius commented May 30, 2018

@enebo I guess I'm saying yes, it probably should :-)

@headius
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headius commented May 30, 2018

@pitr-ch I think we agree. I just wanted to point out this is a rather unlikely scenario. Nearly all code will have at least one call, which will trigger the polling.

@enebo
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enebo commented May 30, 2018

ah yeah times is native. No call here so times is missing the magic itself. Not an IR bug at least.

@headius
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headius commented Jul 18, 2020

The following patch fixes this with a minimum of overhead (only checking thread events every N calls):

diff --git a/core/src/main/java/org/jruby/RubyFixnum.java b/core/src/main/java/org/jruby/RubyFixnum.java
index a97878ce99..6cdcce4c56 100644
--- a/core/src/main/java/org/jruby/RubyFixnum.java
+++ b/core/src/main/java/org/jruby/RubyFixnum.java
@@ -278,17 +278,26 @@ public class RubyFixnum extends RubyInteger implements Constantizable {
                     final IRubyObject nil = context.nil;
                     for (long i = 0; i < value; i++) {
                         block.yieldSpecific(context, nil);
+                        if ((i & ThreadContext.CALL_POLL_COUNT) == 0) {
+                            context.pollThreadEvents();
+                        }
                     }
                 } else {
                     // no arg needed
                     for (long i = 0; i < value; i++) {
                         block.yieldSpecific(context);
+                        if ((i & ThreadContext.CALL_POLL_COUNT) == 0) {
+                            context.pollThreadEvents();
+                        }
                     }
                 }
             } else {
                 final Ruby runtime = context.runtime;
                 for (long i = 0; i < value; i++) {
                     block.yield(context, RubyFixnum.newFixnum(runtime, i));
+                    if ((i & ThreadContext.CALL_POLL_COUNT) == 0) {
+                        context.pollThreadEvents();
+                    }
                 }
             }
             return this;
diff --git a/core/src/main/java/org/jruby/runtime/ThreadContext.java b/core/src/main/java/org/jruby/runtime/ThreadContext.java
index 0318639a2c..7992a3e9e3 100644
--- a/core/src/main/java/org/jruby/runtime/ThreadContext.java
+++ b/core/src/main/java/org/jruby/runtime/ThreadContext.java
@@ -97,7 +97,7 @@ public final class ThreadContext {
     private final static int INITIAL_FRAMES_SIZE = 10;
 
     /** The number of calls after which to do a thread event poll */
-    private final static int CALL_POLL_COUNT = 0xFFF;
+    public final static int CALL_POLL_COUNT = 0xFFF;
 
     // runtime, nil, and runtimeCache cached here for speed of access from any thread
     public final Ruby runtime;

However it does reduce performance to use even the "call" version of polling:

BEFORE:
$ jruby -e "loop { t = Time.now; 100_000_000.times { }; puts Time.now - t }"
0.542925
0.567139
0.627118
0.507028
0.508385
0.512144
0.507685

AFTER:
$ jruby -e "loop { t = Time.now; 100_000_000.times { }; puts Time.now - t }"
0.557857
0.600398
0.593976
0.5913959999999999
0.601807
0.5930259999999999

Note that the performance of a pure-Ruby version, when the stars align (this is on GraalVM), both works and performs well (since the thread interrupt is handled as a safepoint):

BEFORE:
$ jruby -Xcompile.invokedynamic -Xfixnum.cache=false -e "class Integer; def times; i = 0; while i < self; yield i; i += 1; end; end; end; loop { t = Time.now; 100_000_000.times { }; puts Time.now - t }"
0.213364
0.17784799999999998
0.11926099999999999
0.12261899999999999
0.11895299999999999
0.11813799999999999

AFTER:
$ jruby -Xcompile.invokedynamic -Xfixnum.cache=false -e "class Integer; def times; i = 0; while i < self; yield i; i += 1; end; end; end; loop { t = Time.now; 100_000_000.times { }; puts Time.now - t }"
0.158944
0.176442
0.119419
0.122568
0.119013
0.121836

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4 participants
@headius @enebo @subbuss @pitr-ch