Per-isolate v8::Locker and v8::Unlocker

test/cctest/test-lockers.cc

Index: test/cctest/test-lockers.cc
diff --git a/test/cctest/test-lockers.cc b/test/cctest/test-lockers.cc
new file mode 100644
index 0000000000000000000000000000000000000000..3499f7134338f37fac6e09152728292994fa5e77
--- /dev/null
+++ b/test/cctest/test-lockers.cc
@@ -0,0 +1,602 @@
+// Copyright 2007-2009 the V8 project authors. All rights reserved.

[Vitaly Repeshko, 2011/04/15 00:29:39]

2011

[Dmitry Lomov, 2011/04/19 01:50:47]

Done.

+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include <limits.h>
+#include <vector>
+
+#include "v8.h"
+
+#include "api.h"
+#include "isolate.h"
+#include "compilation-cache.h"
+#include "execution.h"
+#include "snapshot.h"
+#include "platform.h"
+#include "utils.h"
+#include "cctest.h"
+#include "parser.h"
+#include "unicode-inl.h"
+
+using ::v8::AccessorInfo;
+using ::v8::Context;
+using ::v8::Extension;
+using ::v8::Function;
+using ::v8::HandleScope;
+using ::v8::Local;
+using ::v8::Object;
+using ::v8::ObjectTemplate;
+using ::v8::Persistent;
+using ::v8::Script;
+using ::v8::String;
+using ::v8::Value;
+using ::v8::V8;
+
+namespace i = ::i;
+
+
+
+
+// Migrating an isolate
+class KangarooThread : public v8::internal::Thread {
+ public:
+  explicit KangarooThread(v8::Isolate* isolate,

[Vitaly Repeshko, 2011/04/15 00:29:39]

nit: explicit not required.

[Dmitry Lomov, 2011/04/19 01:50:47]

Done.

+                               v8::Handle<v8::Context> context, int value)

[Vitaly Repeshko, 2011/04/15 00:29:39]

nit: Weird indentation.

[Dmitry Lomov, 2011/04/19 01:50:47]

Done.

+      : Thread(NULL, "KangarooThread1"),

[Vitaly Repeshko, 2011/04/15 00:29:39]

Why 1? There doesn't seem to be a second one.

[Dmitry Lomov, 2011/04/19 01:50:47]

Done.

+        isolate_(isolate), context_(context), value_(value) {
+  }
+
+  void Run() {
+    {
+      v8::Locker locker(isolate_);
+      v8::Isolate::Scope isolate_scope(isolate_);
+      CHECK_EQ(isolate_, v8::internal::Isolate::Current());
+      v8::HandleScope scope;
+      context_->Enter();

[Vitaly Repeshko, 2011/04/15 00:29:39]

Please use Context::Scope where possible.

[Dmitry Lomov, 2011/04/19 01:50:47]

Done.

+      Local<Value> v = CompileRun("getValue()");
+      CHECK(v->IsNumber());
+      CHECK_EQ(30, static_cast<int>(v->NumberValue()));
+      context_->Exit();
+    }
+    {
+      v8::Locker locker(isolate_);
+      v8::Isolate::Scope isolate_scope(isolate_);
+      context_->Enter();
+      v8::HandleScope scope;
+      Local<Value> v = CompileRun("getValue()");
+      CHECK(v->IsNumber());
+      CHECK_EQ(30, static_cast<int>(v->NumberValue()));
+      context_->Exit();
+    }
+    isolate_->Dispose();
+  }
+
+ private:
+  v8::Isolate* isolate_;
+  Persistent<v8::Context> context_;
+  int value_;
+};
+
+
+TEST(KangarooIsolates) {

[Vitaly Repeshko, 2011/04/15 00:29:39]

Please describe what a test does for non-trivial tests, e.g. "Test migrating an
isolate between the main thread and an additional thread."

+  v8::Isolate* isolate = v8::Isolate::New();
+  Persistent<v8::Context> context;
+  {
+    v8::Locker locker_(isolate);

[Vitaly Repeshko, 2011/04/15 00:29:39]

nit: Why _ ?

[Dmitry Lomov, 2011/04/19 01:50:47]

Done.

+    v8::Isolate::Scope isolate_scope(isolate);
+    v8::HandleScope handle_scope;
+    context = v8::Context::New();
+    context->Enter();
+    CHECK_EQ(isolate, v8::internal::Isolate::Current());
+    CompileRun("function getValue() { return 30; }");

[Vitaly Repeshko, 2011/04/15 00:29:39]

It'd be useful for this script to have some state, e.g. the first time it runs,
it returns "hello from main thread", then --- "hello from kangaroo", etc.

[Dmitry Lomov, 2011/04/19 01:50:47]

It has a state of sorts - note that KangarooThread evaluates a different script
- this one defines a getValue, and KanagrooThread verifies that this function is
defined and returns what it should.
On 2011/04/15 00:29:39, Vitaly Repeshko wrote:

+    context->Exit();
+  }
+  KangarooThread thread1(isolate, context, 1);
+  thread1.Start();
+  thread1.Join();
+}
+
+static void CalcFibAndCheck() {
+  Local<Value> v = CompileRun("function fib(n) {"
+                              "  if (n <= 2) return 1;"
+                              "  return fib(n-1) + fib(n-2);"
+                              "}"
+                              "fib(10)");
+  CHECK(v->IsNumber());
+  CHECK_EQ(55, static_cast<int>(v->NumberValue()));
+}
+
+class JoinableThread : public i::Thread {

[Vitaly Repeshko, 2011/04/15 00:29:39]

To make this a bit more readable make JoinableThread *not* inherit from Thread
and provide Start and Join methods using a hidden per thread semaphore. Use a
hidden inner class to implement Run. Later we could use it to implement Thread
on the platforms that reuse thread ids.

[Dmitry Lomov, 2011/04/19 01:50:47]

Done.

+ public:
+  explicit JoinableThread(i::Isolate* isolate, const char* name)
+    : Thread(isolate, name),
+      semaphore_(NULL) {
+  }
+
+  void StartWithSignal(i::Semaphore* semaphore) {
+    semaphore_ = semaphore;
+    Start();
+  }
+
+  void Run() {

[Vitaly Repeshko, 2011/04/15 00:29:39]

nit: Keep "virtual" when overriding.

[Dmitry Lomov, 2011/04/19 01:50:47]

Done.

+    DoRun();
+    if (semaphore_ != NULL)
+      semaphore_->Signal();
+  }
+  virtual void DoRun() = 0;
+ private:
+  i::Semaphore* semaphore_;
+};
+
+
+class IsolateLockingThreadWithLocalContext : public JoinableThread {
+ public:
+  explicit IsolateLockingThreadWithLocalContext(v8::Isolate* isolate)
+    : JoinableThread(NULL, "IsolateLockingThread"),
+      isolate_(isolate) {
+  }
+
+  void DoRun() {
+    v8::Locker locker(isolate_);
+    v8::Isolate::Scope isolate_scope(isolate_);
+    v8::HandleScope handle_scope;
+    LocalContext local_context;
+    CHECK_EQ(isolate_, v8::internal::Isolate::Current());
+    CalcFibAndCheck();
+  }
+ private:
+  v8::Isolate* isolate_;
+};
+
+static void StartJoinAndDeleteThreads(const i::List<JoinableThread*>& threads) {
+  i::Semaphore* semaphore = i::OS::CreateSemaphore(0);
+  for (int i = 0; i < threads.length(); i++) {
+    threads[i]->StartWithSignal(semaphore);
+  }
+  for (int i = 0; i < threads.length(); i++) {
+    semaphore->Wait();
+  }
+  for (int i = 0; i < threads.length(); i++) {
+    delete threads[i];
+  }
+  delete semaphore;
+}
+
+TEST(IsolateLockingStress) {
+  const int kNThreads = 100;
+  i::List<JoinableThread*> threads(kNThreads);
+  v8::Isolate* isolate = v8::Isolate::New();
+  for (int i = 0; i < kNThreads; i++) {
+    threads.Add(new IsolateLockingThreadWithLocalContext(isolate));
+  }
+  StartJoinAndDeleteThreads(threads);
+  isolate->Dispose();
+}
+
+class IsolateNonlockingThread : public JoinableThread {
+ public:
+  explicit IsolateNonlockingThread()
+    : JoinableThread(NULL, "IsolateNonlockingThread") {
+  }
+
+  void DoRun() {
+    v8::Isolate* isolate = v8::Isolate::New();
+    {
+      v8::Isolate::Scope isolate_scope(isolate);
+      v8::HandleScope handle_scope;
+      v8::Handle<v8::Context> context = v8::Context::New();
+      context->Enter();
+      CHECK_EQ(isolate, v8::internal::Isolate::Current());
+      CalcFibAndCheck();
+     context->Exit();

[Vitaly Repeshko, 2011/04/15 00:29:39]

nit: Fix indentation.

[Dmitry Lomov, 2011/04/19 01:50:47]

Done.

+    }
+    isolate->Dispose();
+  }
+ private:
+};
+
+TEST(MultithreadedParallelIsolates) {
+  const int kNThreads = 50;
+  i::List<JoinableThread*> threads(kNThreads);
+  for (int i = 0; i < kNThreads; i++) {
+    threads.Add(new IsolateNonlockingThread());
+  }
+  StartJoinAndDeleteThreads(threads);
+}
+
+
+class IsolateLockingTwiceThread : public JoinableThread {

[Vitaly Repeshko, 2011/04/15 00:29:39]

LockingTwice -> NestedLocking

[Dmitry Lomov, 2011/04/19 01:50:47]

Done.

+ public:
+  explicit IsolateLockingTwiceThread(v8::Isolate* isolate)
+    : JoinableThread(NULL, "IsolateLockingTwice"), isolate_(isolate) {
+  }
+  void DoRun() {
+    v8::Locker lock(isolate_);
+    v8::Isolate::Scope isolate_scope(isolate_);
+    v8::HandleScope handle_scope;
+    LocalContext local_context;
+    {
+      v8::Locker another_lock(isolate_);
+      CalcFibAndCheck();
+    }
+    {
+      v8::Locker another_lock(isolate_);
+      CalcFibAndCheck();
+    }
+  }
+ private:
+  v8::Isolate* isolate_;
+};
+
+TEST(IsolateLockingTwice) {
+  const int kNThreads = 100;
+  v8::Isolate* isolate = v8::Isolate::New();
+  i::List<JoinableThread*> threads(kNThreads);
+  for (int i = 0; i < kNThreads; i++) {
+    threads.Add(new IsolateLockingTwiceThread(isolate));
+  }
+  StartJoinAndDeleteThreads(threads);
+}
+
+class LockIsolateAndCalculateFibThread : public JoinableThread {

[Vitaly Repeshko, 2011/04/15 00:29:39]

Isn't this the same as IsolateLockingThreadWithLocalContext?

[Dmitry Lomov, 2011/04/19 01:50:47]

Done.

+ public:
+  explicit LockIsolateAndCalculateFibThread(v8::Isolate* isolate)
+    : JoinableThread(NULL, "LockIsolateAndCalculateFibThread"),
+      isolate_(isolate) {
+  }
+
+  void DoRun() {
+    v8::Locker lock(isolate_);
+    v8::Isolate::Scope isolate_scope(isolate_);
+    LocalContext local_context;
+    HandleScope handle_scope;
+    CalcFibAndCheck();
+  }
+ private:
+  v8::Isolate* isolate_;
+};
+
+class SeparateIsolatesLocksNonexclusiveThreadA : public JoinableThread {
+ public:
+  explicit SeparateIsolatesLocksNonexclusiveThreadA(v8::Isolate* isolate1,

[Vitaly Repeshko, 2011/04/15 00:29:39]

nit: explicit not required.

[Dmitry Lomov, 2011/04/19 01:50:47]

Done.

+                                                    v8::Isolate* isolate2)
+    : JoinableThread(NULL, "ASeparateIsolatesLocksNonexclusiveThreadA"),

[Vitaly Repeshko, 2011/04/15 00:29:39]

Why "A"? There doesn't seem to be a "B" variant of this.

[Dmitry Lomov, 2011/04/19 01:50:47]

Done.

+      isolate1_(isolate1), isolate2_(isolate2) {
+  }
+
+  void DoRun() {
+    v8::Locker lock(isolate1_);
+    v8::Isolate::Scope isolate_scope(isolate1_);
+    v8::HandleScope handle_scope;
+    LocalContext local_context;
+
+    LockIsolateAndCalculateFibThread threadB(isolate2_);
+    i::Semaphore* semaphore = i::OS::CreateSemaphore(0);
+    threadB.StartWithSignal(semaphore);
+    CalcFibAndCheck();
+    semaphore->Wait();
+    delete semaphore;
+  }
+ private:
+  v8::Isolate* isolate1_;
+  v8::Isolate* isolate2_;
+};
+
+TEST(SeparateIsolatesLocksNonexclusive) {
+  const int kNThreads = 100;
+  v8::Isolate* isolate1 = v8::Isolate::New();
+  v8::Isolate* isolate2 = v8::Isolate::New();
+  i::List<JoinableThread*> threads(kNThreads);
+  for (int i = 0; i < kNThreads; i++) {
+    threads.Add(new SeparateIsolatesLocksNonexclusiveThreadA(isolate1,
+                                                             isolate2));
+  }
+  StartJoinAndDeleteThreads(threads);
+  isolate2->Dispose();
+  isolate1->Dispose();
+}
+
+class LockIsolateAndCalculateFibSharedContextThread : public JoinableThread {
+ public:
+  explicit LockIsolateAndCalculateFibSharedContextThread(
+      v8::Isolate* isolate, v8::Handle<v8::Context> context)
+    : JoinableThread(NULL, "LockIsolateAndCalculateFibThread"),
+      isolate_(isolate),
+      context_(context) {
+  }
+
+  void DoRun() {
+    v8::Locker lock(isolate_);
+    v8::Isolate::Scope isolate_scope(isolate_);
+    HandleScope handle_scope;
+    context_->Enter();
+    CalcFibAndCheck();
+    context_->Exit();
+  }
+ private:
+  v8::Isolate* isolate_;
+  Persistent<v8::Context> context_;
+};
+
+class LockerUnlockerThread : public JoinableThread {
+ public:
+  explicit LockerUnlockerThread(v8::Isolate* isolate)
+    : JoinableThread(NULL, "LockerUnlockerThread"),
+      isolate_(isolate) {
+  }
+
+  void DoRun() {
+    v8::Locker lock(isolate_);
+    v8::Isolate::Scope isolate_scope(isolate_);
+    v8::HandleScope handle_scope;
+    v8::Handle<v8::Context> context = v8::Context::New();
+    context->Enter();
+    CalcFibAndCheck();
+    {
+      context->Exit();

[Vitaly Repeshko, 2011/04/15 00:29:39]

Do we have to exit the context here?

[Dmitry Lomov, 2011/04/19 01:50:47]

Yes because we exit the isolate - in the next line.

+      isolate_->Exit();
+      v8::Unlocker unlocker(isolate_);

[Vitaly Repeshko, 2011/04/15 00:29:39]

Hmm, do we really want to be able to unlock some arbitrary isolate? Maybe the
unlocker should support only the currently entered isolate and do Exit/Enter for
us?

[Dmitry Lomov, 2011/04/19 01:50:47]

Here is what I think on the subject:
1. I do not have a good real-life use case for Unlocker, so I have to argue from
aesthetics, which is not very convincing
2. Keeping Lock/Unlock and Enter/Exit orthogonal has a nice orthogonality to it
:)
3. Having to exit manually, as in the above code, is a bit on the ugly side;
however Unlocker that automatically exists suffers from two issues:
a) Unlocker unlocks all the Lockers that it is under, but it cannot possibly
exit all the scopes, as in:
  Locker lock(i1);
  i1->Enter();   
  Locker lock2(i1);
  i2->Enter();
  i1->Enter(); 
  Unlocker unlock(I1)
Unlocker can unlock all the locks, but it cannot exit i1 correctly in this case;
and if unlocker automatically exits, the user may be under the impression that
it can.
b) if Unlocker exits, it is only natural that Locker enters. Shall we do that as
well?

On 2011/04/15 00:29:39, Vitaly Repeshko wrote:

+      LockIsolateAndCalculateFibSharedContextThread thread(isolate_, context);
+      i::Semaphore* semaphore = i::OS::CreateSemaphore(0);
+      thread.StartWithSignal(semaphore);
+      semaphore->Wait();
+      delete semaphore;
+    }
+    isolate_->Enter();
+    context->Enter();
+    CalcFibAndCheck();

[Vitaly Repeshko, 2011/04/15 00:29:39]

context->Exit()?

[Dmitry Lomov, 2011/04/19 01:50:47]

Done.

+  }
+ private:
+  v8::Isolate* isolate_;
+};
+
+TEST(LockerUnlocker) {
+  const int kNThreads = 100;
+  i::List<JoinableThread*> threads(kNThreads);
+  v8::Isolate* isolate = v8::Isolate::New();
+  for (int i = 0; i < kNThreads; i++) {
+    threads.Add(new LockerUnlockerThread(isolate));
+  }
+  StartJoinAndDeleteThreads(threads);
+  isolate->Dispose();
+}
+
+class LockTwiceAndUnlockThread : public JoinableThread {
+ public:
+  explicit LockTwiceAndUnlockThread(v8::Isolate* isolate)
+    : JoinableThread(NULL, "LockTwiceAndUnlockThread"),
+      isolate_(isolate) {
+  }
+
+  void DoRun() {
+    v8::Locker lock(isolate_);
+    v8::Isolate::Scope isolate_scope(isolate_);
+    v8::HandleScope handle_scope;
+    v8::Handle<v8::Context> context = v8::Context::New();
+    context->Enter();
+    CalcFibAndCheck();
+    {
+      v8::Locker second_lock(isolate_);
+      {
+        context->Exit();
+        isolate_->Exit();
+        v8::Unlocker unlocker(isolate_);
+        LockIsolateAndCalculateFibSharedContextThread thread(isolate_, context);
+        i::Semaphore* semaphore = i::OS::CreateSemaphore(0);
+        thread.StartWithSignal(semaphore);
+        semaphore->Wait();
+        delete semaphore;
+      }
+    }
+    isolate_->Enter();
+    context->Enter();
+    CalcFibAndCheck();
+  }

[Vitaly Repeshko, 2011/04/15 00:29:39]

context->Exit()?

[Dmitry Lomov, 2011/04/19 01:50:47]

Done.

+ private:
+  v8::Isolate* isolate_;
+};
+
+TEST(LockTwiceAndUnlock) {
+  const int kNThreads = 100;
+  i::List<JoinableThread*> threads(kNThreads);
+  v8::Isolate* isolate = v8::Isolate::New();
+  for (int i = 0; i < kNThreads; i++) {
+    threads.Add(new LockTwiceAndUnlockThread(isolate));
+  }
+  StartJoinAndDeleteThreads(threads);
+  isolate->Dispose();
+}
+
+class LockAndUnlockDifferentIsolatesThread : public JoinableThread {
+ public:
+  LockAndUnlockDifferentIsolatesThread(v8::Isolate* isolate1,
+                                       v8::Isolate* isolate2)
+    : JoinableThread(NULL, "LockAndUnlockDifferentIsolatesThread"),
+      isolate1_(isolate1),
+      isolate2_(isolate2) {
+  }
+
+  void DoRun() {
+    Persistent<v8::Context> context1;
+    Persistent<v8::Context> context2;
+    v8::Locker lock1(isolate1_);
+    CHECK(v8::Locker::IsLocked(isolate1_));
+    CHECK(!v8::Locker::IsLocked(isolate2_));
+    {
+      v8::Isolate::Scope isolate_scope(isolate1_);
+      v8::HandleScope handle_scope;
+      context1 = v8::Context::New();
+      context1->Enter();
+      CalcFibAndCheck();
+      context1->Exit();
+    }
+    v8::Locker lock2(isolate2_);
+    CHECK(v8::Locker::IsLocked(isolate1_));
+    CHECK(v8::Locker::IsLocked(isolate2_));
+    {
+      v8::Isolate::Scope isolate_scope(isolate2_);
+      v8::HandleScope handle_scope;
+      context2 = v8::Context::New();
+      context2->Enter();
+      CalcFibAndCheck();
+      context2->Exit();
+    }
+    {
+      v8::Unlocker unlock1(isolate1_);
+      CHECK(!v8::Locker::IsLocked(isolate1_));
+      CHECK(v8::Locker::IsLocked(isolate2_));
+      v8::Isolate::Scope isolate_scope(isolate2_);
+      v8::HandleScope handle_scope;
+      context2->Enter();
+      i::Semaphore* semaphore = i::OS::CreateSemaphore(0);
+      LockIsolateAndCalculateFibSharedContextThread thread(isolate1_, context1);
+      thread.StartWithSignal(semaphore);
+      CalcFibAndCheck();
+      semaphore->Wait();
+      delete semaphore;
+      context2->Exit();
+    }
+  }
+ private:
+  v8::Isolate* isolate1_;
+  v8::Isolate* isolate2_;
+};
+
+TEST(LockAndUnlockDifferentIsolates) {
+  v8::Isolate* isolate1 = v8::Isolate::New();
+  v8::Isolate* isolate2 = v8::Isolate::New();
+  LockAndUnlockDifferentIsolatesThread thread(isolate1, isolate2);
+  i::Semaphore* semaphore = i::OS::CreateSemaphore(0);
+  thread.StartWithSignal(semaphore);
+  semaphore->Wait();
+  delete semaphore;
+  isolate2->Dispose();
+  isolate1->Dispose();
+}
+
+class LockUnlockLockThread : public JoinableThread {
+ public:
+  LockUnlockLockThread(v8::Isolate* isolate, v8::Handle<v8::Context> context)
+    : JoinableThread(NULL, "LockUnlockLockThread"),
+      isolate_(isolate),
+      context_(context) {
+  }
+
+  void DoRun() {
+    v8::Locker lock1(isolate_);
+    CHECK(v8::Locker::IsLocked(isolate_));
+    CHECK(!v8::Locker::IsLocked());
+    {
+      v8::Isolate::Scope isolate_scope(isolate_);
+      v8::HandleScope handle_scope;
+      context_->Enter();
+      CalcFibAndCheck();
+      context_->Exit();
+    }
+    {
+      v8::Unlocker unlock1(isolate_);
+      CHECK(!v8::Locker::IsLocked(isolate_));
+      CHECK(!v8::Locker::IsLocked());
+      {
+        v8::Locker lock2(isolate_);
+        v8::Isolate::Scope isolate_scope(isolate_);
+        v8::HandleScope handle_scope;
+        CHECK(v8::Locker::IsLocked(isolate_));
+        CHECK(!v8::Locker::IsLocked());
+        context_->Enter();
+        CalcFibAndCheck();
+        context_->Exit();
+      }
+    }
+  }
+
+ private:
+  v8::Isolate* isolate_;
+  v8::Persistent<v8::Context> context_;
+};
+
+TEST(LockUnlockLockMultithreaded) {
+  const int kNThreads = 100;
+  v8::Isolate* isolate = v8::Isolate::New();
+  Persistent<v8::Context> context;
+  {
+    v8::Locker locker_(isolate);
+    v8::Isolate::Scope isolate_scope(isolate);
+    v8::HandleScope handle_scope;
+    context = v8::Context::New();
+  }
+  i::List<JoinableThread*> threads(kNThreads);
+  for (int i = 0; i < kNThreads; i++) {
+    threads.Add(new LockUnlockLockThread(isolate, context));
+  }
+  StartJoinAndDeleteThreads(threads);
+}
+
+class LockUnlockLockDefaultIsolateThread : public JoinableThread {
+ public:
+  LockUnlockLockDefaultIsolateThread(v8::Handle<v8::Context> context)
+    : JoinableThread(NULL, "LockUnlockLockDefaultIsolateThread"),
+      context_(context) {
+  }
+
+  void DoRun() {
+    v8::Locker lock1;
+    {
+      v8::HandleScope handle_scope;
+      context_->Enter();
+      CalcFibAndCheck();
+      context_->Exit();
+    }
+    {
+      v8::Unlocker unlock1;
+      {
+        v8::Locker lock2;
+        v8::HandleScope handle_scope;
+        context_->Enter();
+        CalcFibAndCheck();
+        context_->Exit();
+      }
+    }
+  }
+
+ private:
+  v8::Persistent<v8::Context> context_;
+};
+
+TEST(LockUnlockLockDefaultIsolateMultithreaded) {
+  const int kNThreads = 100;
+  Persistent<v8::Context> context;
+  {
+    v8::Locker locker_;
+    v8::HandleScope handle_scope;
+    context = v8::Context::New();
+  }
+  i::List<JoinableThread*> threads(kNThreads);
+  for (int i = 0; i < kNThreads; i++) {
+    threads.Add(new LockUnlockLockDefaultIsolateThread(context));
+  }
+  StartJoinAndDeleteThreads(threads);
+}