Hello again,
I'm trying to use v8::NativeWeakMap on the global object, and I'm getting
inconsistent results. It looks like "this" (on the outer scope)
and just using plain variables (on the outer scope) get me to two different
places. How is that possible? Here is a sample program:
#include <iostream>
#include <string.h>
#include "libplatform/libplatform.h"
#include "v8/v8.h"
void runit(v8::Isolate *isolate, const char *script_text)
{
std::cout << "------------------------------------------" << std::endl;
std::cout << "/" << script_text << "/ <==" << std::endl;
v8::Local<v8::String> source =
v8::String::NewFromUtf8(isolate,script_text);
v8::Local<v8::Script> script = v8::Script::Compile(source);
v8::Local<v8::Value> result = script->Run();
v8::String::Utf8Value ascii(result);
std::cout << "/" << script_text << "/ ==> " << *ascii << std::endl;
}
v8::Persistent<v8::NativeWeakMap,
v8::CopyablePersistentTraits<v8::NativeWeakMap> > gWeakMap;
void GetNamedAccessor(v8::Local<v8::Name> name, const
v8::PropertyCallbackInfo<v8::Value>& info)
{
std::cout << "[" << std::hex << info.This()->GetIdentityHash() << "]
GetNamedAccessor, name=" << *v8::String::Utf8Value(name) << std::endl;
}
void SetNamedAccessor(v8::Local<v8::Name> name, v8::Local<v8::Value> value,
const v8::PropertyCallbackInfo<void>& info)
{
std::cout << "[" << std::hex << info.This()->GetIdentityHash() << "]
SetNamedAccessor, name=" << *v8::String::Utf8Value(name)
<< ", value=" << *v8::String::Utf8Value(value) << std::endl;
auto myWeakMap =
v8::Local<v8::NativeWeakMap>::New(info.GetIsolate(),gWeakMap);
v8::Local<v8::Value> val = myWeakMap->Get(info.This());
std::cout << "[ weak map holds " << *v8::String::Utf8Value(val) << " ]"
<< std::endl;
}
class ArrayBufferAllocator : public v8::ArrayBuffer::Allocator {
public:
virtual void* Allocate(size_t length) {
std::cout << "!!! Allocate runs !!! length = " << length << std::endl;
void* data = AllocateUninitialized(length);
return data == NULL ? data : memset(data, 0, length);
}
virtual void* AllocateUninitialized(size_t length) { return
malloc(length); }
virtual void Free(void* data, size_t) { free(data); }
};
int main(int argc, char* argv[])
{
// initialize v8
v8::V8::InitializeICU();
v8::V8::InitializeExternalStartupData(argv[0]);
v8::Platform* platform = v8::platform::CreateDefaultPlatform();
v8::V8::InitializePlatform(platform);
v8::V8::Initialize();
ArrayBufferAllocator allocator;
v8::Isolate::CreateParams create_params;
create_params.array_buffer_allocator = &allocator;
auto isolate = v8::Isolate::New(create_params);
v8::Isolate::Scope isolate_scope(isolate);
v8::HandleScope handle_scope(isolate);
auto context = v8::Context::New(isolate);
auto glob = context->Global();
v8::Context::Scope context_scope(context);
// set up the map
auto myWeakMap = v8::NativeWeakMap::New(isolate);
auto vvvStr = v8::String::NewFromUtf8(isolate,"vvv");
myWeakMap->Set(glob, vvvStr);
gWeakMap.Reset(isolate,myWeakMap);
// create accessor
auto onStr = v8::String::NewFromUtf8(isolate,"on");
glob->SetAccessor(onStr, GetNamedAccessor, SetNamedAccessor);
// do some testing
runit(isolate,"this.on = 1");
runit(isolate,"on = 2");
return 0;
}
When I run it, I get this output:
------------------------------------------
/this.on = 1/ <==
[37cec19f] SetNamedAccessor, name=on, value=1
[ weak map holds vvv ]
/this.on = 1/ ==> 1
------------------------------------------
/on = 2/ <==
[3c587822] SetNamedAccessor, name=on, value=2
[ weak map holds undefined ]
/on = 2/ ==> 2
As you can see, the hash value for the second case is different, and
theNativeWeakMap doesn't work at all.
Please note, that the named accessor works properly in both cases.
Any ideas why this is happening?
On Thursday, May 12, 2016 at 12:37:13 PM UTC+3, Jochen Eisinger wrote:
>
> You can e.g. create a v8::NativeWeakMap and map from the object to
> whatever private value you want to store on it.
>
> The map won't keep the object alive, but if it's GC'd, the entry is
> deleted automatically.
>
> On Wed, May 11, 2016 at 9:45 AM Danny Dorfman <[email protected]
> <javascript:>> wrote:
>
>> Hello Jochen,
>>
>> I tried caching the keys after creating them using ForApi(), and this is
>> somewhat faster.
>> Still, I see that the GetPrivate/SetPrivate API's are considerably slower
>> than their Get/Set counterparts.
>> What did you mean by maintaining a weak map? Can you please be more
>> specific?
>>
>> Thank you in advance.
>>
>>
>> On Friday, May 6, 2016 at 9:58:38 AM UTC+3, Jochen Eisinger wrote:
>>
>>> You don't have to use ForApi() to create privates, you can create the
>>> once and then keep them around as keys.
>>>
>>> Another alternative is to maintain a weak map from the objects to your
>>> properties.
>>>
>>> On Thu, May 5, 2016 at 2:46 PM Danny Dorfman <[email protected]>
>>> wrote:
>>>
>> Hello there,
>>>>
>>>> I am looking for a time-efficient way to store private (hidden) values
>>>> in an object. I get key-value pairs
>>>> (where key is of type v8::String and value of type v8::Value), and I
>>>> need to attach them to existing objects.
>>>>
>>>> What I came up with so far - is using v8::Object's SetPrivate()
>>>> function. The only problem with it, is that this method
>>>> takes a v8::Private as its first argument. There is a costly conversion
>>>> between v8::String to v8::Private (using the ForApi method).
>>>> Performance goes down, and after profiling with callgrind, I see that
>>>> ForApi is taking up too many cycles.
>>>>
>>>> Is there a quicker way to accomplish this? (I am running 4.9)
>>>>
>>>> Regards,
>>>> Danny
>>>>
>>>> --
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>>>>
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>>>
>>>
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