Added memory allocation routines for arrays, that we somehow suddenly need and created a Platform implementation that we need for garbage collection to function properly

Author: Martijn Otto

isolate.cpp

@@ -18,6 +18,9 @@
  *  Dependencies
  */
 #include "isolate.h"
+#include "platform.h"
+#include <cstring>
+#include <cstdlib>
 
 /**
  *  Start namespace
@@ -27,14 +30,62 @@ namespace JS {
 /**
  *  Private class
  */
-class Isolate final
+class Isolate final : private v8::ArrayBuffer::Allocator
 {
 private:
+    /**
+     *  The "platform" we run on
+     *  @var    Platform
+     */
+    Platform _platform;
+
+    /**
+     *  The isolate creation parameters
+     *  @var    v8::Isolate::CreateParams
+     */
+    v8::Isolate::CreateParams _params;
+
     /**
      *  The underlying isolate
      *  @var    v8::Isolate*
      */
     v8::Isolate *_isolate;
+
+    /**
+     *  Allocate a range of memory, zero-initialized.
+     *
+     *  @param  size    The number of bytes to allocate
+     *  @return Pointer to the allocated memory, or a nullptr
+     */
+    void *Allocate(size_t size) override
+    {
+        // request some cleared memory
+        return std::calloc(size, 1);
+    }
+
+    /**
+     *  Allocate a range of memory, uninitialized.
+     *
+     *  @param  size    The number of bytes to allocate
+     *  @return Pointer to the allocated memory, or a nullptr
+     */
+    void *AllocateUninitialized(size_t size) override
+    {
+        // request some uninitialized memory
+        return std::malloc(size);
+    }
+
+    /**
+     *  Free some allocated memory
+     *
+     *  @param  data    Pointer to memory to free
+     *  @param  size    Number of bytes to free
+     */
+    void Free(void *data, size_t size) override
+    {
+        // free the allocated memory
+        std::free(data);
+    }
 public:
     /**
      *  Constructor
@@ -43,10 +94,14 @@ class Isolate final
     {
         // initialize the ICU and v8 engine
         v8::V8::InitializeICU();
+        v8::V8::InitializePlatform(&_platform);
         v8::V8::Initialize();
 
+        // initialize the parameters
+        _params.array_buffer_allocator = this;
+
         // create the actual isolate
-        _isolate = v8::Isolate::New();
+        _isolate = v8::Isolate::New(_params);
 
         // and enter it
         _isolate->Enter();
@@ -65,6 +120,9 @@ class Isolate final
 
         // and shut down the engine (this also takes care of the ICU)
         v8::V8::Dispose();
+
+        // finally shut down the platform
+        v8::V8::ShutdownPlatform();
     }
 
     /**

platform.cpp

@@ -0,0 +1,150 @@
+/**
+ *  platform.cpp
+ *
+ *  A "platform" as needed by the v8 engine, implementing
+ *  functionality required for, amongst other things,
+ *  garbage collection.
+ *
+ *  @copyright 2015 Copernica B.V.
+ */
+
+/**
+ *  Dependencies
+ */
+#include "platform.h"
+#include <time.h>
+
+/**
+ *  Start namespace
+ */
+namespace JS {
+
+/**
+ *  Constructor
+ */
+Platform::Platform() :
+    _running(true),
+    _worker(&Platform::run, this)
+{}
+
+/**
+ *  Destructor
+ */
+Platform::~Platform()
+{
+    // we are no longer running
+    _running = false;
+
+    // signal the thread in case it is waiting for input
+    _condition.notify_one();
+
+    // and wait for the thread to stop
+    _worker.join();
+}
+
+/**
+ *  Execute some work, this is called
+ *  by the worker thread to keep going
+ */
+void Platform::run()
+{
+    // keep going indefinitely
+    while (true)
+    {
+        // lock the work queue
+        std::unique_lock<std::mutex> lock(_mutex);
+
+        // wait for new work to arrive
+        while (_tasks.empty() && _running) _condition.wait(lock);
+
+        // still no tasks? we must be done
+        if (!_running) return;
+
+        // retrieve the new task
+        auto *task = _tasks.front();
+
+        // remove it from the queue
+        _tasks.pop_front();
+
+        // unlock the queue again
+        lock.unlock();
+
+        // execute the task
+        task->Run();
+
+        // and clean it up
+        delete task;
+    }
+}
+
+/**
+ *  Schedule a task to be executed on a background thread.
+ *
+ *  The platform takes responsibility for the task, and will
+ *  free it when the task has finished executing.
+ *
+ *  @param  task    The task to execute
+ *  @param  time    The expected run time
+ */
+void Platform::CallOnBackgroundThread(v8::Task *task, ExpectedRuntime time)
+{
+    // lock the mutex
+    _mutex.lock();
+
+    // add the task to the list
+    _tasks.push_back(task);
+
+    // unlock the mutex again
+    _mutex.unlock();
+
+    // signal the worker that work is ready
+    _condition.notify_one();
+}
+
+/**
+ *  Schedule a task to be executed on a foreground thread.
+ *
+ *  @param  isolate The isolate the task belongs to
+ *  @param  task    The task to execute
+ */
+void Platform::CallOnForegroundThread(v8::Isolate *isolate, v8::Task *task)
+{
+    /**
+     *  We are _required_ to implement this function, as it is a pure-virtual
+     *  in the v8::Platform class. It is, however, never called, unless one
+     *  calls the PumpMessageLoop method, in which case it would not work
+     *  either, since that function blindly casts it to a DefaultPlatform
+     *  object and executes the PumpMessageLoop on this object.
+     *
+     *  Besides the fact that the cast would fail, and the function call
+     *  thus ends in a segfault, there is no way to fix this even without
+     *  this weird casting, since the PumpMessageLoop is not a virtual
+     *  function.
+     *
+     *  Because of this I hereby declare this function to be utterly
+     *  useless. It can never be called, but we can't compile without.
+     */
+}
+
+/**
+ *  Retrieve the monotonically increasing time. The starting point
+ *  is not relevant, but it must return at least millisecond-precision
+ *
+ *  @return time in seconds since an unspecified time
+ */
+double Platform::MonotonicallyIncreasingTime()
+{
+    // the result structure
+    struct timespec time;
+
+    // retrieve the current time
+    clock_gettime(CLOCK_MONOTONIC_RAW, &time);
+
+    // convert the result to a double with millisecond precision
+    return static_cast<double>(time.tv_sec) + static_cast<double>(time.tv_nsec) / 1000000000;
+}
+
+/**
+ *  End namespace
+ */
+}

platform.h

@@ -0,0 +1,114 @@
+/**
+ *  platform.h
+ *
+ *  A "platform" as needed by the v8 engine, implementing
+ *  functionality required for, amongst other things,
+ *  garbage collection.
+ *
+ *  @copyright 2015 Copernica B.V.
+ */
+
+/**
+ *  Include guard
+ */
+#pragma once
+
+/**
+ *  Dependencies
+ */
+#include <v8-platform.h>
+#include <condition_variable>
+#include <atomic>
+#include <thread>
+#include <mutex>
+#include <deque>
+
+/**
+ *  Start namespace
+ */
+namespace JS {
+
+/**
+ *  Class definition
+ */
+class Platform : public v8::Platform
+{
+private:
+    /**
+     *  The list of tasks to execute
+     *  @var    std::queue<Task*>
+     */
+    std::deque<v8::Task*> _tasks;
+
+    /**
+     *  Are we still supposed to be running?
+     *  @var    std::atomic<bool>
+     */
+    std::atomic<bool> _running;
+
+    /**
+     *  Mutex to protect the task list
+     *  @var    std::mutex
+     */
+    std::mutex _mutex;
+
+    /**
+     *  Condition variable to signal new work arriving
+     *  @var    std::condition_variable
+     */
+    std::condition_variable _condition;
+
+    /**
+     *  The worker thread
+     *  @var    std::thread
+     */
+    std::thread _worker;
+
+    /**
+     *  Execute some work, this is called
+     *  by the worker thread to keep going
+     */
+    void run();
+public:
+    /**
+     *  Constructor
+     */
+    Platform();
+
+    /**
+     *  Destructor
+     */
+    virtual ~Platform();
+
+    /**
+     *  Schedule a task to be executed on a background thread.
+     *
+     *  The platform takes responsibility for the task, and will
+     *  free it when the task has finished executing.
+     *
+     *  @param  task    The task to execute
+     *  @param  time    The expected run time
+     */
+    void CallOnBackgroundThread(v8::Task *task, ExpectedRuntime time) override;
+
+    /**
+     *  Schedule a task to be executed on a foreground thread.
+     *
+     *  @param  isolate The isolate the task belongs to
+     *  @param  task    The task to execute
+     */
+    void CallOnForegroundThread(v8::Isolate *isolate, v8::Task *task) override;
+
+    /**
+     *  Retrieve the monotonically increasing time. The starting point
+     *  is not relevant, but it must return at least millisecond-precision
+     *
+     *  @return time in milliseconds since an unspecified time
+     */
+    double MonotonicallyIncreasingTime() override;
+};
+
+/**
+ *  End namespace
+ */
+}