Hello, Yes, while your handles are in an handle scope they will not be deleted. So in your case you do not need to use a persistent handle.
You must use a persistent handle only in case you want to keep an object which is no longer in a handle context. For example, if you got the handle on a callback function from the main thread then you use it from an other thread, you must use a persistent handle, to make sure it will not be deleted while there is no handle context holding it. About the persistent handle, be careful to release it : http://izs.me/v8-docs/classv8_1_1Persistent.html#a33e53191844272ba0f2da4f55fc12297 Loïc Le vendredi 14 août 2015 21:33:24 UTC+8, Andy C a écrit : > > Maybe it is not as bad as I thought. I missed a bit of a sentence in the > V8 embedder's guide: > > When the destructor, HandleScope::~HandleScope, is called the handle scope >> is deleted. Objects referred to by handles within the deleted handle scope >> are eligible for removal in the next garbage collection *if there are no >> other references to them*. > > > I *think* this means that because fs.writeFile() has a reference to the > Buffer, it will not be garbage collected, and the memory held on to. > > Andy > > > On Thursday, 13 August 2015 23:09:39 UTC+1, Andy C wrote: >> >> Hi, >> I am writing a C++ module for node. I have a JS callback registered which >> will receive regular callbacks with binary data (audio data). >> >> My C++ to call the callback looks a bit like: >> >> UniquePersistent<v8::Function> dataCallback = // from somewhere... >> >> HandleScope scope(isolate); >> >> const unsigned argc = 1; >> auto buffer = node::Buffer::New(dataSize); >> std::memcpy(node::Buffer::Data(buffer), data.get(), dataSize); >> >> Local<Value> argv[argc] = { buffer }; >> >> auto fn = Local<Function>::New(isolate, dataCallback); >> auto context = isolate->GetCurrentContext(); >> auto global = context->Global(); >> fn->Call(global, argc, argv); >> >> At the moment my callback is simply passing the buffer on to >> fs.writeFile(...): >> >> var fs = require('fs'); >> mymodule.dosomething(function(data) { >> fs.writeFile('raw_data', data, { flag: 'a' }) >> }); >> >> This appears to work, however the lifetime of the buffer object is >> suspect. This seems unsafe, as my understanding is that the Local<Buffer> >> is going to be cleared up when the HandleScope is destroyed after the >> callback has returned. Unfortunately, fs.writeFile() is probably still busy >> with the buffer. >> >> The key would seem to be something to do with Persistent<> and >> UniquePersistent<> but I don't quite grok it. >> >> Any tips, or pointers to examples would be great... >> >> >> -- Job board: http://jobs.nodejs.org/ New group rules: https://gist.github.com/othiym23/9886289#file-moderation-policy-md Old group rules: https://github.com/joyent/node/wiki/Mailing-List-Posting-Guidelines --- You received this message because you are subscribed to the Google Groups "nodejs" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/nodejs/2a2317c9-84f7-4c3f-8944-586f72758ed0%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
