ZeroCopy messaging is something that can be implemented in zeromq, but is it possible to use it with the zmqpp c++ bindings? There is almost no documentation, and I was not able to find anything in the examples...
I would switch to cppzmq.
It's a more active project and maintained by some of the core libzmq people.
It's header only and has support for zero copy.
Just simply use zmqpp::message::copy().
In the zmqpp source code we can see:
void message::copy(message const& source)
{
_parts.resize( source._parts.size() );
for(size_t i = 0; i < source._parts.size(); ++i)
{
_parts[i] = source._parts[i].copy();
}
// we don't need a copy of the releasers as we did data copies of the internal data,
//_releasers = source._releasers;
//_strings = source._strings
}
the _parts which defined as:
private:
typedef std::vector<frame> parts_type;
parts_type _parts;
so, source._parts[i].copy() actually call zmqpp::frame::copy() which defined here:
frame frame::copy() const
{
frame other( size() );
other._sent = _sent;
if( 0 != zmq_msg_copy( &other._msg, const_cast<zmq_msg_t*>(&_msg) ) )
{
throw zmq_internal_exception();
}
return other;
}
zmqpp::frame::_msg in the code snippet is defined as zmq_msg_t. All zmq_msg_t object in the frame objects of source zmqpp::message object been zero copied by zmq_msg_copy to new zmqpp::message object.
so, zmqpp::message::copy() help us get a new zmqpp::message object which it's all frame is zero copied from the source zmqpp::message object.
Related
I implement a wrapper around the Google V8 engine. I wrote a class:
class Es
{
public:
Es();
~Es();
int Init(const char* exec_path);
int CreateContext(uint& id);
int RemoveContext(const uint id);
protected:
Global<Context> global_context;
std::map<uint, Persistent<Context>*> contexts;
Isolate* isolate = nullptr;
private:
uint next_id = 1;
};
I want to create Contexts, hold them in the contexts var, and remove them oneday. So, I init the V8 engine:
int Es::Init(const char* exec_path)
{
v8::V8::InitializeICUDefaultLocation(exec_path);
v8::V8::InitializeExternalStartupData(exec_path);
std::unique_ptr<Platform> platform = platform::NewDefaultPlatform();
V8::InitializePlatform(platform.get());
V8::Initialize();
Isolate::CreateParams create_params;
create_params.array_buffer_allocator = ArrayBuffer::Allocator::NewDefaultAllocator();
isolate = Isolate::New(create_params);
if (!isolate)
return InitError;
return Success;
}
And after that I want to create a context, using int Es::CreateContext(uint& id). Its called after Init.
int EasyProspect::CreateContext(uint& id)
{
if (!isolate)
return NotInitializedError;
Isolate::Scope isolate_scope(isolate);
HandleScope handle_scope(isolate);
Local<Context> local_context = Context::New(isolate);
Persistent<Context> context(isolate, local_context);
contexts.emplace(id, &context);
return Success;
}
But I can't do that, the code crashes on Context::New(isolate). Why? isolate is not null, I enter the local scope...
Your best bet is to compile in Debug mode and run in a debugger. Then it should be easy to tell what's causing the crash.
(At the very least, you should post a complete reproducible example, including specifying the V8 version you're working with, how that's built/configured, and how you're compiling your code.)
If I had to guess: the Platform and the ArrayBuffer::Allocator need to stay alive for as long as you want to use the V8 instance, but in your code they are both destroyed at the end of Es::Init. Since Es is a wrapper class, you can easily add fields there to keep them around.
This post is about exposing C++ objects to the v8 javascript engine. To attach a C++ object to a javascript object, I make use of the GetInternalField() and External APIs. Before you can set or get any internal field, you have to call SetInternalFieldCount() on the corresponding ObjectTemplate. Since I want to expose a constructor function to the JS, I created a FunctionTemplate, set a C++ function that attache the native object to the JS object to that template, and finally SetInternalCount() on the InstanceTemplate() of that function template. Too much words for the description, here is what I did:
struct Point {
int x, y;
Local<FunctionTemplate> CreatePointContext(Isolate* isolate) {
Local<FunctionTemplate> constructor = FunctionTemplate::New(isolate, &ConstructorCallback);
constructor->InstanceTemplate()->SetInternalFieldCount(1); // I set internal field count here.
constructor->SetClassName(String::NewFromUtf8(isolate, "Point", NewStringType::kInternalized).ToLocalChecked());
auto prototype_t = constructor->PrototypeTemplate();
prototype_t->SetAccessor(String::NewFromUtf8(isolate, "x", NewStringType::kInternalized).ToLocalChecked(),
XGetterCallback);
return constructor;
};
// This callback is bound to the constructor to attach a C++ Point instance to js object.
static void ConstructorCallback(const FunctionCallbackInfo<Value>& args) {
auto isolate = args.GetIsolate();
Local<External> external = External::New(isolate, new Point);
args.Holder()->SetInternalField(0, external);
}
// This callback retrieves the C++ object and extract its 'x' field.
static void XGetterCallback(Local<String> property, const PropertyCallbackInfo<Value>& info) {
auto external = Local<External>::Cast(info.Holder()->GetInternalField(0)); // This line triggers an out-of-bound error.
auto point = reinterpret_cast<Point*>(external->Value());
info.GetReturnValue().Set(static_cast< double>(point->x));
}
// This function creates a context that install the Point function template.
Local<Context> CreatePointContext(Isolate* isolate) {
auto global = ObjectTemplate::New(isolate);
auto point_ctor = Point::CreateClassTemplate(isolate);
global->Set(isolate, "Point", point_ctor);
return Context::New(isolate, nullptr, global);
}
When I tried to run the following JS code with the exposed C++ object, I got Internal field out of bounds error.
var p = new Point();
p.x;
I wonder setting internal field count on the instance template of a function template has nothing to do with the object created by the new expression. If so, what is the correct way to set the internal field count of the object created by new while exposing the constructor function to javascript? I want to achieve the following 2 things:
In javascript, a Point function is avaible so we can var p = new Point;.
In C++ I can make sure the JS object has 1 internal field for our C++ Point to live in.
Edit: As #snek pointed out, I changed Holder() to This() and everything started to work. But later When I changed SetAccessor to SetAccessorProperty, it worked even with Holder.
Although the behaviour are very confusing, I think the major problem may not lie in the difference between Holder and This, but rather in SetAccessor and SetAccessorProperty. Why? Because in many docs I have read, Holder should be identical to This in most cases and I believe without using Signature and given that my testing js code is so simple (not with any magic property moving), in my case This should just be Holder.
Thus I decided to post another question about SetAccessor and SetAccessorProperty and leave this post as a reference.
For why I am so sure about in my case This() == Holder() should hold, here are some old threads:
https://groups.google.com/forum/#!topic/v8-users/fK9PBWxJxtQ
https://groups.google.com/forum/#!topic/v8-users/Axf4hF_RfZo
And what does the docs say?
/**
* If the callback was created without a Signature, this is the same
* value as This(). If there is a signature, and the signature didn't match
* This() but one of its hidden prototypes, this will be the respective
* hidden prototype.
*
* Note that this is not the prototype of This() on which the accessor
* referencing this callback was found (which in V8 internally is often
* referred to as holder [sic]).
*/
V8_INLINE Local<Object> Holder() const;
Note in my code there is not Signature, literally. So This and Holder should make no difference, but with SetAccessor, they made a difference.
#include <queue>
struct model_shell_t
{
model_shell_t() {clear();}
void clear();
void Release() {clear(); model_pool._delete(this);}
void SetArgument(byte4 _type, byte4 _arg1, byte4 _arg2)
{
switch( _type )
{
case 100:
if( tail_enable && !_arg1 )
{
tail_deque.clear();//tail_queue.c.clear(); // Error C2248 Cannot access protected member of queue
}
tail_enable = _arg1;
break;
case 101:
tail_interval = _arg1;
tail_count = _arg2;
break;
}
}
queue<model_t> tail_queue;
byte4 tail_enable;
byte4 tail_interval;
byte4 tail_count;
deque<model_t> tail_deque;
};
Another :
for( byte4 i = 0; i < ms->tail_queue.size(); i++ )
{
//ms->tail_queue.c[i].bind_model = &bind_ms->tail_queue.c[i];
ms->tail_deque[i].bind_model = &bind_ms->tail_deque[i];
}
error C2248: 'std::queue<_Ty>::c' : cannot access protected member
declared in class 'std::queue<_Ty>'
When i upgrade solution from VS2003 to VS2008 i cant use clear() function.
How can i use it ?
Thank you
EDITED : With help from Igor Tandetnik i have change above
VS2003 was wrong, VS2008 is right. The underlying container should be a protected member, and shouldn't be accessible. Your code relies on a non-conforming implementation detail - essentially, on a compiler bug that has since been fixed.
As you apparently need direct access to elements, you are breaking queue abstraction anyway. It'd be easiest to just use std::deque directly, without a wrapper.
If for some reason you insist on using std::queue, another approach would be for model_shell_t to privately derive from it, rather than having it as a member. This way it'll have direct access to c. Though it's unclear why you would want to take such a circuitous route to getting a std::deque member.
I'm stuck on this one.
Given three variables:
an IDispatch* to a connectable object
the IID (DIID) of an outgoing dispinterface on that object
the name of a member defined by the dispinterface
How can resolve the name to a DISPID?
pDispatch->GetIDsOfNames(...) returns DISP_E_UNKNOWNNAME, as I would expect (outgoing interfaces aren't implemented by the connectable object)
I need to support scenarios where 0 clients have yet connected to the outgoing interface, so I can't enumerate the existing connection points in order to call GetIDsOfNames on one of them (I'm not even sure this would work)
In order to perform manual reflection, I would need the dispinterface's ITypeInfo. I could get this from the coclass's ITypeInfo. However pDispatch->GetTypeInfo(0, ...) returns the ITypeInfo for the IDispatch implementation (as per the documentation), not the ITypeInfo for the coclass. (And there are no other ITypeInfos exposed by this object's IDispatch implementation.)
If the object is "quite standard", then it should be possible.
From the object/IDispatch interface, you should be able to get to the TLB (type library). From the type library, you should be able to browse all coclasses, and get interfaces that these coclasses implement. You need to get to interface you have the IID for, browse the member and get the one you're interested.
There are many cases where this just won't work. Here is a console sample I've put up that works with a shell object. I've written it in C# because it's easier, but there's nothing you can't do with a decent language. I've used an old TLBINF32.DLL com utility library (only x86 unfortunately) I talk about in my answer to this question here on SO: How to read COM TypeLib with C# or C++?
static void Main(string[] args)
{
// create a sample object every one has
object o = Activator.CreateInstance(Type.GetTypeFromProgID("shell.application")); // for example
TLIApplication app = new TLIApplication();
// not sure, but I believe in pure COM it's calling IDispatch::GetTypeInfo & ITypeInfo::GetContainingTypeLib
TypeLibInfo tli = app.InterfaceInfoFromObject(o).Parent;
// this is the guid for DShellFolderViewEvents
int dispid = GetDispId(tli, new Guid("{62112AA2-EBE4-11CF-A5FB-0020AFE7292D}"), "SelectionChanged");
Console.WriteLine("dispid:" + dispid); // should display 200
}
public static int GetDispId(TypeLibInfo tlb, Guid diid, string memberName)
{
// browse all coclasses
// in pure COM this is ITypeLib::GetTypeInfo
foreach (CoClassInfo ti in tlb.CoClasses)
{
// browse all interfaces in those coclasses
// in pure COM this is ITypeInfo::GetRefTypeOfImplType
foreach (InterfaceInfo itf in ti.Interfaces)
{
// only select [source] interfaces (events)
// this test is optional since the diid is unique
// in pure COM this is ITypeInfo::GetImplTypeFlags
if (((ImplTypeFlags)itf.AttributeMask & ImplTypeFlags.IMPLTYPEFLAG_FSOURCE) != ImplTypeFlags.IMPLTYPEFLAG_FSOURCE)
continue;
if (new Guid(itf.GUID) == diid)
{
// in pure COM this is ITypeInfo::GetTypeAttr & ITypeInfo::GetFuncDesc
foreach (MemberInfo mi in itf.Members)
{
if (mi.Name == memberName)
return mi.MemberId;
}
}
}
}
return -1;
}
Is it possible to set a custom allocator for OpenCV 2.3.1? I have a memory pool created and I want OpenCV to use that pool for what it needs.
Is that possible?
If it is, how can it be done?
Updated:
I made some developments since last answer, but I still have some problems.
This is the code I have now:
CvAllocFunc allocCV()
{
return (CvAllocFunc) MEMPOOL->POOLalloc(sz);
}
CvFreeFunc deallocCV()
{
return (CvFreeFunc) MEMPOOL->POOLfree(ptr);
}
...
cvSetMemoryManager(allocCV(),deallocCV(),data);
Now, my question is, how can I have access to the size and the pointer to the data I want to allocate and later to deallocate?
Just found out:
The version of OpenCV I'm using (2.3.1) throws an error when using cvSetMemoryManager. The reason is in its source code:
void cvSetMemoryManager( CvAllocFunc, CvFreeFunc, void * )
{
CV_Error( -1, "Custom memory allocator is not supported" );
}
I was very disappointed with this. I guess I can't use a custom memory pool with OpenCV anymore!
Right from the docs
http://opencv.willowgarage.com/documentation/c/core_utility_and_system_functions_and_macros.html#setmemorymanager
Use the
void cvSetMemoryManager(CvAllocFunc allocFunc=NULL, CvFreeFunc freeFunc=NULL, void* userdata=NULL)
function.
Your code
cvSetMemoryManager(allocCV(),deallocCV(),data);
is WRONG.
See what happens: you call allocCV and deallocCV functions (they return some pointer which is quietly converted to cvAllocFunc) !
And this is only the beginning. See the docs for alloc/dealloc semantics. You should write allocCV/deallocCV with correct signatures.
void* CV_CDECL allocCV(size_t size, void* userdata)
{
return ((YourMemPoolTypeWhichIDoNotKnow*)userdata)->POOLalloc(size);
}
int CV_CDECL deallocCV(void* pptr, void* userdata)
{
return ((YourMemPoolTypeWhichIDoNotKnow*)userdata)->POOLfree(pptr);
}
and then pass your MEMPOOL in the 'userdata' parameter:
cvSetMemoryManager(&allocCV, &deallocCV, (void*)MEMPOOL);
This is a standard way for a library to provide user callbacks.