tools/android/webgpu/src/main/cpp/JNIContext.h

// Copyright 2024 The Dawn & Tint Authors
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#ifndef WEBGPU_JNI_JNICONTEXT_H_
#define WEBGPU_JNI_JNICONTEXT_H_

#include <jni.h>
#include <type_traits>
#include <utility>
#include <vector>

#include "dawn/common/NonMovable.h"

namespace dawn::kotlin_api {

// A helper context class to use while processing JNI calls.
//
//  - Frees memory that's allocated (or referenced) during the processing of the call.
//
// TODO(330293719): Consider using a bump allocator for Alloc/AllocArray. Since we require that the
// types allocated have a default destructor, we could just free a few large allocations instead of
// small ones. We could also allocate the first bytes on the stack itself.
class JNIContext : dawn::NonMovable {
  public:
    explicit JNIContext(JNIEnv* env);
    ~JNIContext();

    // Public members for convenience.
    JNIEnv* const env;

    const char* GetStringUTFChars(jstring s);
    const jint* GetIntArrayElements(jintArray a);

    template <typename T>
    T* Alloc() {
        static_assert(std::is_trivially_destructible_v<T>);
        static_assert(std::is_trivially_constructible_v<T>);
        T* alloc = new T();
        mAllocationsToFree.push_back(alloc);
        return alloc;
    }

    template <typename T>
    T* AllocArray(size_t count) {
        static_assert(std::is_trivially_destructible_v<T>);
        static_assert(std::is_trivially_constructible_v<T>);
        T* alloc = new T[count]();
        mArrayAllocationsToFree.push_back(alloc);
        return alloc;
    }

  private:
    std::vector<std::pair<jstring, const char*>> mStringsToRelease;
    std::vector<std::pair<jintArray, jint*>> mIntArraysToRelease;
    std::vector<void*> mAllocationsToFree;
    std::vector<void*> mArrayAllocationsToFree;
};

}  // namespace dawn::kotlin_api

#endif  // WEBGPU_JNI_JNICONTEXT_H_