Mozilla/mozilla/js2/src/gc_allocator.h

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 *
 * The contents of this file are subject to the Netscape Public
 * License Version 1.1 (the "License"); you may not use this file
 * except in compliance with the License. You may obtain a copy of
 * the License at http://www.mozilla.org/NPL/
 *
 * Software distributed under the License is distributed on an "AS
 * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express oqr
 * implied. See the License for the specific language governing
 * rights and limitations under the License.
 *
 * The Original Code is the JavaScript 2 Prototype.
 *
 * The Initial Developer of the Original Code is Netscape
 * Communications Corporation.  Portions created by Netscape are
 * Copyright (C) 1998 Netscape Communications Corporation. All
 * Rights Reserved.
 *
 * Contributor(s): 
 *
 * Alternatively, the contents of this file may be used under the
 * terms of the GNU Public License (the "GPL"), in which case the
 * provisions of the GPL are applicable instead of those above.
 * If you wish to allow use of your version of this file only
 * under the terms of the GPL and not to allow others to use your
 * version of this file under the NPL, indicate your decision by
 * deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL.  If you do not delete
 * the provisions above, a recipient may use your version of this
 * file under either the NPL or the GPL.
 */

#ifndef gc_allocator_h
#define gc_allocator_h

#include <memory>

// Microsoft VC6 bug: standard identifiers should be in std namespace
#ifndef _WIN32
using std::size_t;
using std::ptrdiff_t;
#endif

namespace JavaScript {
    extern "C" {
        void* GC_malloc(size_t bytes);
        void* GC_malloc_atomic(size_t bytes);
        void GC_free(void* ptr);
        void GC_gcollect(void);

        typedef void (*GC_finalization_proc) (void* obj, void* client_data);
        void GC_register_finalizer(void* obj, GC_finalization_proc proc,
                                   void* client_data,
                                   GC_finalization_proc *old_proc,
                                   void* *old_client_data);
    }

#if 0 && !defined(XP_MAC)
    // for platforms where GC doesn't exist yet.
    inline void* GC_malloc(size_t bytes) { return ::operator new(bytes); }
    inline void* GC_malloc_atomic(size_t bytes) { return ::operator new(bytes); }
    inline void GC_free(void* ptr) { operator delete(ptr); }
    inline void GC_gcollect() {}
    inline void GC_register_finalizer(void* obj, GC_finalization_proc proc,
                                      void* client_data,
                                      GC_finalization_proc *old_proc,
                                      void* *old_client_data) {}
#endif
    
    /**
     * General case:  memory for type must be allocated as a conservatively
     * scanned block of memory.
     */
    template <class T> struct gc_traits {
        static T* allocate(size_t n) {
            return static_cast<T*>(GC_malloc(n * sizeof(T)));
        }
    };
    
    /**
     * Specializations for blocks of atomic types:  the macro define_atomic_type(_type)
     * specializes gc_traits<T> for types that need not be scanned by the
     * GC. Implementors are free to define other types as atomic, if they are
     * guaranteed not to contain pointers.
     */
#define define_atomic_type(_type)                                               \
    template <> struct gc_traits<_type> {                                       \
        static _type* allocate(size_t n)                                        \
        {                                                                       \
            return static_cast<_type*>(GC_malloc_atomic(n * sizeof(_type)));    \
        }                                                                       \
    };
    
    define_atomic_type(char)
    define_atomic_type(unsigned char)
    define_atomic_type(short)
    define_atomic_type(unsigned short)
    define_atomic_type(int)
    define_atomic_type(unsigned int)
    define_atomic_type(long)
    define_atomic_type(unsigned long)
    define_atomic_type(float)
    define_atomic_type(double)
    
    #undef define_atomic_type
    
    /**
     * Traits for classes that need to have their destructor called
     * when reclaimed by the garbage collector.
     */
    template <class T> struct gc_traits_finalizable {
        static void finalizer(void* obj, void* client_data)
        {
            T* t = static_cast<T*>(obj);
            size_t n = reinterpret_cast<size_t>(client_data);
            for (size_t i = 0; i < n; ++i)
                t[i].~T();
        }
        
        static T* allocate(size_t n)
        {
            T* t = gc_traits<T>::allocate(n);
            GC_finalization_proc old_proc; void* old_client_data;
            GC_register_finalizer(t, &finalizer, reinterpret_cast<void*>(n),
                                  &old_proc, &old_client_data);
            return t;
        }
    };
    
    /**
     * An allocator that can be used to allocate objects in the garbage
     * collected heap.
     */
    template <class T, class traits = gc_traits<T> > class gc_allocator {
    public:
        typedef T value_type;
        typedef size_t size_type;
        typedef ptrdiff_t difference_type;
        typedef T *pointer;
        typedef const T *const_pointer;
        typedef T &reference;
        typedef const T &const_reference;
        
        gc_allocator() {}
        template<typename U, typename UTraits>
        gc_allocator(const gc_allocator<U, UTraits>&) {}
        // ~gc_allocator() {}

        static pointer address(reference r) { return &r; }
        static const_pointer address(const_reference r) { return &r; }
                
        static pointer allocate(size_type n, const void* /* hint */ = 0) {
            return traits::allocate(n);
        }
        static void deallocate(pointer, size_type) {}
        
        static void construct(pointer p, const T &val) { new(p) T(val);}
        static void destroy(pointer p) { p->~T(); }
        
#if defined(__GNUC__) || defined(_WIN32)
        static size_type max_size() { return size_type(-1) / sizeof(T); }
#else
        static size_type max_size() {
            return std::numeric_limits<size_type>::max() / sizeof(T);
        }
#endif

        template<class U> struct rebind { typedef gc_allocator<U> other; };

#ifdef _WIN32
        // raw byte allocator used on some platforms (grrr).
        typedef char _Char[1];
        static char* _Charalloc(size_type n) {
            return (char*) rebind<_Char>::other::allocate(n);
        }

        /**
         * funky operator required for calling basic_string<T> constructor
         * (grrr).
         */
        template<typename U, typename UTraits>
        int operator==(const gc_allocator<U, UTraits>&) { return 0; }
#endif

        // void* deallocate used on some platforms (grrr).
        static void deallocate(void*, size_type) {}

        static void collect() { GC_gcollect(); }
    };

    /**
     * Generic base class for objects allocated using a gc_allocator. How they
     * are allocated can be controlled by specializing gc_traits for the
     * specific class.
     */
    template <typename T> class gc_object {
    public:
        void* operator new(size_t) { return gc_allocator<T>::allocate(1, 0); }
        void operator delete(void* /* ptr */) {}
    };

    /**
     * Simpler base class for classes that have no need to specialize allocation
     * behavior.
     */
    class gc_base {
    public:
        void* operator new(size_t n) { return GC_malloc(n); }
        void operator delete(void*) {}
    };
}

#endif /* gc_allocator_h */