gecko/js/src/nanojit/Allocator.h

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#ifndef __nanojit_Allocator__
#define __nanojit_Allocator__

namespace nanojit
{
    /**
     * Allocator is a bump-pointer allocator with an SPI for getting more
     * memory from embedder-implemented allocator, such as malloc()/free().
     *
     * allocations never return NULL.  The implementation of allocChunk()
     * is expected to perform a longjmp or exception when an allocation can't
     * proceed.
     */
    class Allocator {
    public:
        Allocator();
        ~Allocator();
        void reset();

        /** alloc memory, never return null. */
        void* alloc(size_t nbytes) {
            nbytes = (nbytes + 7) & ~7; // round up
            if (current_top + nbytes <= current_limit) {
                void *p = current_top;
                current_top += nbytes;
                return p;
            }
            return allocSlow(nbytes);
        }

    protected:
        void* allocSlow(size_t nbytes);
        void fill(size_t minbytes);

        class Chunk {
        public:
            Chunk* prev;
            int64_t data[1]; // int64_t forces 8-byte alignment.
        };

        Chunk* current_chunk;
        char* current_top;
        char* current_limit;

        // allocator SPI

        /** allocate another block from a host provided allocator */
        void* allocChunk(size_t nbytes);

        /** free back to the same allocator */
        void freeChunk(void*);

        /** hook for post-reset action. */
        void postReset();
    };
}

/** global new overload enabling this pattern:  new (allocator) T(...) */
inline void* operator new(size_t size, nanojit::Allocator &a) {
    return a.alloc(size);
}

/** global new overload enabling this pattern:  new (allocator) T(...) */
inline void* operator new(size_t size, nanojit::Allocator *a) {
    return a->alloc(size);
}

/** global new[] overload enabling this pattern: new (allocator) T[] */
inline void* operator new[](size_t size, nanojit::Allocator& a) {
    return a.alloc(size);
}

/** global new[] overload enabling this pattern: new (allocator) T[] */
inline void* operator new[](size_t size, nanojit::Allocator* a) {
    return a->alloc(size);
}

#endif // __nanojit_Allocator__