Merge pull request jruby#9226 from headius/narrow_fiber_deadlock_check

Narrow deadlock check for sibling fibers locking mutex

Author: headius

core/src/main/java/org/jruby/ext/thread/Mutex.java

@@ -106,7 +106,8 @@ public IRubyObject lock(ThreadContext context) {
 
         checkRelocking(context);
 
-        if (this.lockingThread == parentThread) {
+        RubyThread lockingThread = this.lockingThread;
+        if (lockingThread == parentThread && context.getFiber() != lockingThread.getContext().getFiber()) {
             throw context.runtime.newThreadError("deadlock; lock already owned by another fiber belonging to the same thread");
         }
 
@@ -123,7 +124,7 @@ public IRubyObject lock(ThreadContext context) {
             }
         }
 
-        this.lockingThread = thread;
+        this.lockingThread = parentThread;
 
         // always check for thread interrupts after acquiring lock
         try {
@@ -204,7 +205,7 @@ public IRubyObject owned_p(ThreadContext context) {
 
     private void checkRelocking(ThreadContext context) {
         if (lock.isHeldByCurrentThread()) {
-            throw context.runtime.newThreadError("Mutex relocking by same thread");
+            throw context.runtime.newThreadError("deadlock; recursive locking");
         }
     }
 

spec/ruby/core/mutex/lock_spec.rb

@@ -20,11 +20,32 @@
 
   # Unable to find a specific ticket but behavior change may be
   # related to this ML thread.
-  it "raises a ThreadError when used recursively" do
+  it "raises a deadlock ThreadError when used recursively" do
     m = Mutex.new
     m.lock
     -> {
       m.lock
-    }.should raise_error(ThreadError)
+    }.should raise_error(ThreadError, /deadlock/)
+  end
+
+  it "raises a deadlock ThreadError when multiple fibers from the same thread try to lock" do
+    m = Mutex.new
+
+    m.lock
+    f0 = Fiber.new do
+      m.lock
+    end
+    -> { f0.resume }.should raise_error(ThreadError, /deadlock/)
+
+    m.unlock
+    f1 = Fiber.new do
+      m.lock
+      Fiber.yield
+    end
+    f2 = Fiber.new do
+      m.lock
+    end
+    f1.resume
+    -> { f2.resume }.should raise_error(ThreadError, /deadlock/)
   end
 end