Fix Monitor#exit when monitor is not owned by current thread

Author: andrykonchin

CHANGELOG.md

@@ -42,6 +42,7 @@ Bug fixes:
 * Don't trigger the `method_added` event when changing a method's visibility or calling `module_function` (@paracycle, @nirvdrum).
 * Fix `rb_time_timespec_new` function to not call `Time.at` method directly (@andrykonchin).
 * Fix `StringIO#write` to transcode strings with encodings that don't match the `StringIO`'s `external_encoding`. (#2839, @flavorjones)
+* Fix `Monitor#exit` to raise `ThreadError` when monitor not owned by the current thread (#2922, @andrykonchin).
 
 Compatibility:
 

spec/ruby/library/monitor/exit_spec.rb

@@ -0,0 +1,10 @@
+require_relative '../../spec_helper'
+require 'monitor'
+
+describe "Monitor#exit" do
+  it "raises ThreadError when monitor is not entered" do
+    m = Monitor.new
+
+    -> { m.exit }.should raise_error(ThreadError)
+  end
+end

src/main/java/org/truffleruby/core/monitor/TruffleMonitorNodes.java

@@ -78,8 +78,10 @@ protected Object enter(RubyMutex mutex) {
     public abstract static class MonitorExit extends PrimitiveArrayArgumentsNode {
 
         @Specialization
-        protected Object exit(RubyMutex mutex) {
+        protected Object exit(RubyMutex mutex,
+                @Cached BranchProfile errorProfile) {
             final RubyThread thread = getLanguage().getCurrentThread();
+            MutexOperations.checkOwnedMutex(getContext(), mutex.lock, this, errorProfile);
             MutexOperations.unlock(mutex.lock, thread);
             return mutex;
         }

src/main/java/org/truffleruby/core/mutex/MutexOperations.java

@@ -100,6 +100,7 @@ public static void internalLockEvenWithException(RubyContext context, ReentrantL
         }
     }
 
+    /** Should be preceded with MutexOperations.checkOwnedMutex call to throw a proper exception */
     @TruffleBoundary
     public static void unlock(ReentrantLock lock, RubyThread thread) {
         unlockInternal(lock);