[futex] Allow debugger to break in the middle of a futexWait

test/cctest/test-debug.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // 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
@@ skipping 18 matching lines @@
 
 #include "src/v8.h"
 
 #include "src/api.h"
 #include "src/base/platform/condition-variable.h"
 #include "src/base/platform/platform.h"
 #include "src/compilation-cache.h"
 #include "src/debug/debug.h"
 #include "src/deoptimizer.h"
 #include "src/frames.h"
+#include "src/futex-emulation.h"
 #include "src/utils.h"
 #include "test/cctest/cctest.h"
 
 
 using ::v8::base::Mutex;
 using ::v8::base::LockGuard;
 using ::v8::base::ConditionVariable;
 using ::v8::base::OS;
 using ::v8::base::Semaphore;
 using ::v8::internal::EmbeddedVector;
@@ skipping 7594 matching lines @@
   CompileRun("function foo() {}; foo();");
   --after_compile_handler_depth;
 }
 
 
 TEST(NoInterruptsInDebugListener) {
   DebugLocalContext env;
   v8::Debug::SetDebugEventListener(NoInterruptsOnDebugEvent);
   CompileRun("void(0);");
 }
+
+
+Barriers futex_barriers;
+
+
+class FutexV8Thread : public v8::base::Thread {
+ public:
+  FutexV8Thread(void* sab_data, size_t sab_size)
+      : Thread(Options("V8Thread")), sab_data_(sab_data), sab_size_(sab_size) {}
+  void Run();
+  v8::Isolate* isolate() { return isolate_; }
+
+ private:
+  v8::Isolate* isolate_;
+  void* sab_data_;
+  size_t sab_size_;
+};
+
+
+class FutexDebuggerThread : public v8::base::Thread {
+ public:
+  explicit FutexDebuggerThread(v8::Isolate* v8_isolate, void* sab_data,
+                               size_t sab_size)
+      : Thread(Options("DebuggerThread")),
+        v8_isolate_(v8_isolate),
+        sab_data_(sab_data),
+        sab_size_(sab_size) {}
+  void Run();
+
+ private:
+  v8::Isolate* v8_isolate_;
+  void* sab_data_;
+  size_t sab_size_;
+};
+
+
+static void FutexMessageHandler(const v8::Debug::Message& message) {
+  static char print_buffer[1000];
+  v8::String::Value json(message.GetJSON());
+  Utf16ToAscii(*json, json.length(), print_buffer);
+  if (IsBreakEventMessage(print_buffer)) {
+    // Check that we are inside the futex.
+    int source_line = GetSourceLineFromBreakEventMessage(print_buffer);
+    CHECK(source_line == 1);
+    futex_barriers.barrier_2.Wait();
+  }
+}
+
+
+void FutexV8Thread::Run() {
+  const char* source =
+      "var i32a = new Int32Array(sab);\n"
+      "Atomics.futexWait(i32a, 0, 0, Infinity)\n";
+
+  v8::Isolate::CreateParams create_params;
+  create_params.array_buffer_allocator = CcTest::array_buffer_allocator();
+  isolate_ = v8::Isolate::New(create_params);
+  futex_barriers.barrier_3.Wait();
+  {
+    v8::Isolate::Scope isolate_scope(isolate_);
+    DebugLocalContext env(isolate_);
+    v8::HandleScope scope(isolate_);
+    v8::Debug::SetMessageHandler(&FutexMessageHandler);
+    v8::Handle<v8::ObjectTemplate> global_template =
+        v8::ObjectTemplate::New(env->GetIsolate());
+    global_template->Set(
+        v8::String::NewFromUtf8(env->GetIsolate(), "sab"),
+        v8::SharedArrayBuffer::New(isolate_, sab_data_, sab_size_));
+
+    v8::Handle<v8::Context> context =
+        v8::Context::New(isolate_, NULL, global_template);
+    v8::Context::Scope context_scope(context);
+
+    CompileRun(source);
+  }
+  futex_barriers.barrier_4.Wait();
+  isolate_->Dispose();
+}
+
+
+void FutexDebuggerThread::Run() {
+  v8::Isolate::CreateParams create_params;
+  create_params.array_buffer_allocator = CcTest::array_buffer_allocator();
+  v8::Isolate* debug_isolate = v8::Isolate::New(create_params);
+  {
+    v8::Isolate::Scope isolate_scope(debug_isolate);
+    DebugLocalContext env(debug_isolate);
+    v8::HandleScope scope(debug_isolate);
+    v8::Handle<v8::SharedArrayBuffer> sab(
+        v8::SharedArrayBuffer::New(debug_isolate, sab_data_, sab_size_));
+
+    i::Handle<i::JSArrayBuffer> i_sab = v8::Utils::OpenHandle(*sab);
+    i::Isolate* i_isolate = reinterpret_cast<i::Isolate*>(debug_isolate);
+    // Spin loop until v8 thread is waiting on futex.
+    while (true) {
+      i::Object* num_waiters =
+          i::FutexEmulation::NumWaitersForTesting(i_isolate, i_sab, 0);
+      if (num_waiters->IsSmi() && i::Smi::cast(num_waiters)->value() > 0) {
+        break;
+      }
+    }
+
+    v8::Debug::DebugBreak(v8_isolate_);
+    futex_barriers.barrier_2.Wait();
+
+    i::FutexEmulation::Wake(i_isolate, i_sab, 0, 1);
+    {
+      const int kBufferSize = 1000;
+      uint16_t buffer[kBufferSize];
+      const char* command_continue =

[binji, 2015/09/16 17:21:13]

It sounds like Yang will be OoO for a month. He didn't want me to use the JSON
protocol here, and use the JS API instead, but I can't see how to do that.

Do either of you know?

+          "{\"seq\":0,"
+          "\"type\":\"request\","
+          "\"command\":\"continue\"}";
+
+      v8::Debug::SendCommand(v8_isolate_, buffer,
+                             AsciiToUtf16(command_continue, buffer));
+    }
+    futex_barriers.barrier_4.Wait();
+  }
+  debug_isolate->Dispose();
+}
+
+
+TEST(FutexDebugging) {
+  i::FLAG_harmony_sharedarraybuffer = true;
+
+  size_t size = 16;
+  v8::ArrayBuffer::Allocator* array_buffer_allocator =
+      CcTest::array_buffer_allocator();
+  void* data = array_buffer_allocator->Allocate(size);
+
+  FutexV8Thread v8_thread(data, size);
+
+  // Create a V8 environment
+  v8_thread.Start();
+  futex_barriers.barrier_3.Wait();
+  FutexDebuggerThread debugger_thread(v8_thread.isolate(), data, size);
+  debugger_thread.Start();
+
+  v8_thread.Join();
+  debugger_thread.Join();
+  array_buffer_allocator->Free(data, size);
+}