On Thu, Jun 27, 2019 at 5:05 AM Austin Einter <austin.ein...@gmail.com> wrote:
>
> Dear All
> I am quite new to v8. I am a c developer, with limited c++ knowledge. Sorry
> if I ask very basic questions.
>
> I have a C application, that interacts with web servers. Gets javascript.
> Need to execute javascript.
> Imagine a situation, where I get total 2 javascript files from server.
>
> js1.js
>
> function js_add_elements(var1, var2)
> {
> var var3 = parseInt(var1) + parseInt(var2);
> var result = 'Addition of ' + var1 + ' and ' + var2 + ' results ' + var3;
> return result;
> }
>
>
> js2.js
>
> js_add_elements(2, 3);
>
>
>
> I have my c code as below.
>
> Header file
> typedef struct
> {
> std::unique_ptr<v8::Platform> platform;
> v8::Isolate::CreateParams create_params;
> v8::Isolate *isolate;
> v8::Isolate::Scope *isolate_scope;
> }MJSEInstance;
>
> #ifdef __cplusplus
> extern "C" {
> #endif
>
> /**
> * @brief Create MJSE instance
> */
> void *mjse_create_instance(char **argv);
>
> /**
> * @brief Destroy MJSE instance
> * @param instance -> MJSE instance
> */
> void mjse_destroy_instance(void *instance);
>
> /**
> * @brief Executes a script
> * @param minstance - MJSE instance
> * @param jscript - the javascript
> * @param scriptlen - Length of script
> */
> void mjse_execute_script(void *instance, char *jscript);
>
> #ifdef __cplusplus
> }
> #endif
>
> CPP File
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include "include/libplatform/libplatform.h"
> #include "include/v8.h"
> #include "mjse.h"
> #include "mjse_int.h"
> #include <new>
>
> extern "C" {
> using namespace v8;
>
> void *mjse_create_instance(char **argv)
> {
> MJSEInstance *instance = (MJSEInstance *)calloc(1, sizeof(MJSEInstance));
>
> v8::V8::InitializeICUDefaultLocation(argv[0]);
> v8::V8::InitializeExternalStartupData(argv[0]);
> instance->platform = v8::platform::NewDefaultPlatform();
>
> v8::V8::InitializePlatform(instance->platform.get());
> v8::V8::Initialize();
>
> instance->create_params.array_buffer_allocator =
> v8::ArrayBuffer::Allocator::NewDefaultAllocator();
> instance->isolate = v8::Isolate::New(instance->create_params);
> instance->isolate_scope = new v8::Isolate::Scope(instance->isolate);
>
> return instance;
> }
>
> void mjse_destroy_instance(void *minstance)
> {
> MJSEInstance *instance = (MJSEInstance *)minstance;
>
> if(instance == NULL)
> return;
>
> if(instance->isolate_scope)
> {
> delete instance->isolate_scope;
> }
>
> if(instance->isolate)
> {
> instance->isolate->Dispose();
> }
>
> v8::V8::Dispose();
> v8::V8::ShutdownPlatform();
>
> if(instance->create_params.array_buffer_allocator)
> {
> delete instance->create_params.array_buffer_allocator;
> }
>
> instance->~MJSEInstance();
> free(instance);
> }
>
>
> void mjse_execute_script(void *minstance, char *jscript)
> {
> MJSEInstance *instance = (MJSEInstance *)minstance;
>
> // Create a stack-allocated handle scope.
> v8::HandleScope handle_scope(instance->isolate);
>
> // Create a new context.
> v8::Local<v8::Context> context = v8::Context::New(instance->isolate);
>
> // Enter the context for compiling and running the hello world script.
> v8::Context::Scope context_scope(context);
>
> {
>
> // Create a string containing the JavaScript source code.
> v8::Local<v8::String> source =
> v8::String::NewFromUtf8(instance->isolate, jscript,
> v8::NewStringType::kNormal).ToLocalChecked();
>
> // Compile the source code.
> v8::Local<v8::Script> script =
> v8::Script::Compile(context, source).ToLocalChecked();
>
> // Run the script to get the result.
> v8::Local<v8::Value> result = script->Run(context).ToLocalChecked();
>
> // Convert the result to an UTF8 string and print it.
> v8::String::Utf8Value utf8(instance->isolate, result);
> printf("%s\n", *utf8);
> }
> }
> }
>
> Main File
> int main(int argc, char **argv)
> {
> char *script;
> void *instance;
>
> instance = mjse_create_instance(argv);
>
> script = "function js_add_elements(var1, var2) \
> { \
> var var3 = parseInt(var1) + parseInt(var2); \
> var result = 'Addition of ' + var1 + ' and ' + var2 + '
> results ' + var3; \
> return result; \
> };";
> mjse_execute_script(instance, script);
>
> script = "js_add_elements(2, 3);";
> mjse_execute_script(instance, script);
>
> mjse_destroy_instance(instance);
> return 0;
> }
>
> Now whats happening, while executing javascript first time it executes fine.
> But while trying to execute second time (letter in red), it gets exception.
>
> I understand, it is creating new v8 Local context each time, and does not
> have js1.js details, hence getting exception. I also found in web we can have
> v8 Global context and refer the context while executing for second time.
>
> However I have not been able to find, how to declare v8 global context and
> store / move v8 local context there and refer it during second time
> execution. Please let me know with a sample/example code.
>
> Thanks
> Austin
You can make the context persistent like this:
if (instance->context == nullptr) {
v8::Local<v8::Context> context = v8::Context::New(instance->isolate);
instance->context = new v8::Global<v8::Context>(instance->isolate, context);
}
v8::Local<v8::Context> context(instance->isolate, instance->context);
v8::Context::Scope context_scope(context);
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