Initial revision
This commit is contained in:
Akinori Ito
516
gc/gcc_support.c
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516
gc/gcc_support.c
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/***************************************************************************
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Interface between g++ and Boehm GC
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Copyright (c) 1991-1995 by Xerox Corporation. All rights reserved.
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THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
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OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
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Permission is hereby granted to copy this code for any purpose,
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provided the above notices are retained on all copies.
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Last modified on Sun Jul 16 23:21:14 PDT 1995 by ellis
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This module provides runtime support for implementing the
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Ellis/Detlefs GC proposal, "Safe, Efficient Garbage Collection for
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C++", within g++, using its -fgc-keyword extension. It defines
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versions of __builtin_new, __builtin_new_gc, __builtin_vec_new,
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__builtin_vec_new_gc, __builtin_delete, and __builtin_vec_delete that
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invoke the Bohem GC. It also implements the WeakPointer.h interface.
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This module assumes the following configuration options of the Boehm GC:
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-DALL_INTERIOR_POINTERS
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-DDONT_ADD_BYTE_AT_END
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This module adds its own required padding to the end of objects to
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support C/C++ "one-past-the-object" pointer semantics.
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****************************************************************************/
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#include <stddef.h>
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#include "gc.h"
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#if defined(__STDC__)
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# define PROTO( args ) args
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#else
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# define PROTO( args ) ()
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# endif
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#define BITSPERBYTE 8
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/* What's the portable way to do this? */
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typedef void (*vfp) PROTO(( void ));
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extern vfp __new_handler;
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extern void __default_new_handler PROTO(( void ));
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/* A destructor_proc is the compiler generated procedure representing a
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C++ destructor. The "flag" argument is a hidden argument following some
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compiler convention. */
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typedef (*destructor_proc) PROTO(( void* this, int flag ));
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/***************************************************************************
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A BI_header is the header the compiler adds to the front of
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new-allocated arrays of objects with destructors. The header is
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padded out to a double, because that's what the compiler does to
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ensure proper alignment of array elements on some architectures.
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int NUM_ARRAY_ELEMENTS (void* o)
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returns the number of array elements for array object o.
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char* FIRST_ELEMENT_P (void* o)
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returns the address of the first element of array object o.
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***************************************************************************/
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typedef struct BI_header {
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int nelts;
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char padding [sizeof( double ) - sizeof( int )];
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/* Better way to do this? */
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} BI_header;
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#define NUM_ARRAY_ELEMENTS( o ) \
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(((BI_header*) o)->nelts)
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#define FIRST_ELEMENT_P( o ) \
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((char*) o + sizeof( BI_header ))
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/***************************************************************************
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The __builtin_new routines add a descriptor word to the end of each
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object. The descriptor serves two purposes.
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First, the descriptor acts as padding, implementing C/C++ pointer
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semantics. C and C++ allow a valid array pointer to be incremented
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one past the end of an object. The extra padding ensures that the
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collector will recognize that such a pointer points to the object and
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not the next object in memory.
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Second, the descriptor stores three extra pieces of information,
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whether an object has a registered finalizer (destructor), whether it
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may have any weak pointers referencing it, and for collectible arrays,
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the element size of the array. The element size is required for the
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array's finalizer to iterate through the elements of the array. (An
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alternative design would have the compiler generate a finalizer
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procedure for each different array type. But given the overhead of
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finalization, there isn't any efficiency to be gained by that.)
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The descriptor must be added to non-collectible as well as collectible
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objects, since the Ellis/Detlefs proposal allows "pointer to gc T" to
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be assigned to a "pointer to T", which could then be deleted. Thus,
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__builtin_delete must determine at runtime whether an object is
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collectible, whether it has weak pointers referencing it, and whether
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it may have a finalizer that needs unregistering. Though
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GC_REGISTER_FINALIZER doesn't care if you ask it to unregister a
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finalizer for an object that doesn't have one, it is a non-trivial
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procedure that does a hash look-up, etc. The descriptor trades a
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little extra space for a significant increase in time on the fast path
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through delete. (A similar argument applies to
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GC_UNREGISTER_DISAPPEARING_LINK).
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For non-array types, the space for the descriptor could be shrunk to a
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single byte for storing the "has finalizer" flag. But this would save
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space only on arrays of char (whose size is not a multiple of the word
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size) and structs whose largest member is less than a word in size
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(very infrequent). And it would require that programmers actually
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remember to call "delete[]" instead of "delete" (which they should,
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but there are probably lots of buggy programs out there). For the
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moment, the space savings seems not worthwhile, especially considering
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that the Boehm GC is already quite space competitive with other
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malloc's.
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Given a pointer o to the base of an object:
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Descriptor* DESCRIPTOR (void* o)
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returns a pointer to the descriptor for o.
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The implementation of descriptors relies on the fact that the GC
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implementation allocates objects in units of the machine's natural
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word size (e.g. 32 bits on a SPARC, 64 bits on an Alpha).
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**************************************************************************/
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typedef struct Descriptor {
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unsigned has_weak_pointers: 1;
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unsigned has_finalizer: 1;
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unsigned element_size: BITSPERBYTE * sizeof( unsigned ) - 2;
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} Descriptor;
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#define DESCRIPTOR( o ) \
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((Descriptor*) ((char*)(o) + GC_size( o ) - sizeof( Descriptor )))
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/**************************************************************************
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Implementations of global operator new() and operator delete()
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***************************************************************************/
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void* __builtin_new( size )
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size_t size;
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/*
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For non-gc non-array types, the compiler generates calls to
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__builtin_new, which allocates non-collected storage via
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GC_MALLOC_UNCOLLECTABLE. This ensures that the non-collected
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storage will be part of the collector's root set, required by the
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Ellis/Detlefs semantics. */
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{
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vfp handler = __new_handler ? __new_handler : __default_new_handler;
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while (1) {
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void* o = GC_MALLOC_UNCOLLECTABLE( size + sizeof( Descriptor ) );
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if (o != 0) return o;
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(*handler) ();}}
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void* __builtin_vec_new( size )
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size_t size;
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/*
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For non-gc array types, the compiler generates calls to
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__builtin_vec_new. */
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{
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return __builtin_new( size );}
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void* __builtin_new_gc( size )
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size_t size;
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/*
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For gc non-array types, the compiler generates calls to
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__builtin_new_gc, which allocates collected storage via
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GC_MALLOC. */
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{
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vfp handler = __new_handler ? __new_handler : __default_new_handler;
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while (1) {
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void* o = GC_MALLOC( size + sizeof( Descriptor ) );
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if (o != 0) return o;
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(*handler) ();}}
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void* __builtin_new_gc_a( size )
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size_t size;
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/*
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For non-pointer-containing gc non-array types, the compiler
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generates calls to __builtin_new_gc_a, which allocates collected
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storage via GC_MALLOC_ATOMIC. */
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{
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vfp handler = __new_handler ? __new_handler : __default_new_handler;
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while (1) {
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void* o = GC_MALLOC_ATOMIC( size + sizeof( Descriptor ) );
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if (o != 0) return o;
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(*handler) ();}}
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void* __builtin_vec_new_gc( size )
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size_t size;
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/*
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For gc array types, the compiler generates calls to
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__builtin_vec_new_gc. */
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{
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return __builtin_new_gc( size );}
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void* __builtin_vec_new_gc_a( size )
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size_t size;
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/*
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For non-pointer-containing gc array types, the compiler generates
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calls to __builtin_vec_new_gc_a. */
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{
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return __builtin_new_gc_a( size );}
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static void call_destructor( o, data )
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void* o;
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void* data;
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/*
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call_destructor is the GC finalizer proc registered for non-array
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gc objects with destructors. Its client data is the destructor
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proc, which it calls with the magic integer 2, a special flag
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obeying the compiler convention for destructors. */
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{
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((destructor_proc) data)( o, 2 );}
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void* __builtin_new_gc_dtor( o, d )
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void* o;
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destructor_proc d;
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/*
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The compiler generates a call to __builtin_new_gc_dtor to register
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the destructor "d" of a non-array gc object "o" as a GC finalizer.
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The destructor is registered via
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GC_REGISTER_FINALIZER_IGNORE_SELF, which causes the collector to
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ignore pointers from the object to itself when determining when
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the object can be finalized. This is necessary due to the self
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pointers used in the internal representation of multiply-inherited
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objects. */
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{
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Descriptor* desc = DESCRIPTOR( o );
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GC_REGISTER_FINALIZER_IGNORE_SELF( o, call_destructor, d, 0, 0 );
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desc->has_finalizer = 1;}
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static void call_array_destructor( o, data )
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void* o;
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void* data;
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/*
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call_array_destructor is the GC finalizer proc registered for gc
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array objects whose elements have destructors. Its client data is
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the destructor proc. It iterates through the elements of the
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array in reverse order, calling the destructor on each. */
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{
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int num = NUM_ARRAY_ELEMENTS( o );
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Descriptor* desc = DESCRIPTOR( o );
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size_t size = desc->element_size;
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char* first_p = FIRST_ELEMENT_P( o );
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char* p = first_p + (num - 1) * size;
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if (num > 0) {
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while (1) {
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((destructor_proc) data)( p, 2 );
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if (p == first_p) break;
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p -= size;}}}
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void* __builtin_vec_new_gc_dtor( first_elem, d, element_size )
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void* first_elem;
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destructor_proc d;
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size_t element_size;
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/*
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The compiler generates a call to __builtin_vec_new_gc_dtor to
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register the destructor "d" of a gc array object as a GC
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finalizer. "first_elem" points to the first element of the array,
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*not* the beginning of the object (this makes the generated call
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to this function smaller). The elements of the array are of size
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"element_size". The destructor is registered as in
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_builtin_new_gc_dtor. */
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{
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void* o = (char*) first_elem - sizeof( BI_header );
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Descriptor* desc = DESCRIPTOR( o );
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GC_REGISTER_FINALIZER_IGNORE_SELF( o, call_array_destructor, d, 0, 0 );
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desc->element_size = element_size;
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desc->has_finalizer = 1;}
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void __builtin_delete( o )
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void* o;
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/*
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The compiler generates calls to __builtin_delete for operator
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delete(). The GC currently requires that any registered
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finalizers be unregistered before explicitly freeing an object.
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If the object has any weak pointers referencing it, we can't
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actually free it now. */
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{
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if (o != 0) {
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Descriptor* desc = DESCRIPTOR( o );
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if (desc->has_finalizer) GC_REGISTER_FINALIZER( o, 0, 0, 0, 0 );
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if (! desc->has_weak_pointers) GC_FREE( o );}}
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void __builtin_vec_delete( o )
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void* o;
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/*
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The compiler generates calls to __builitn_vec_delete for operator
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delete[](). */
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{
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__builtin_delete( o );}
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/**************************************************************************
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Implementations of the template class WeakPointer from WeakPointer.h
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***************************************************************************/
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typedef struct WeakPointer {
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void* pointer;
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} WeakPointer;
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void* _WeakPointer_New( t )
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void* t;
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{
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if (t == 0) {
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return 0;}
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else {
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void* base = GC_base( t );
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WeakPointer* wp =
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(WeakPointer*) GC_MALLOC_ATOMIC( sizeof( WeakPointer ) );
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Descriptor* desc = DESCRIPTOR( base );
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wp->pointer = t;
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desc->has_weak_pointers = 1;
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GC_general_register_disappearing_link( &wp->pointer, base );
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return wp;}}
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static void* PointerWithLock( wp )
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WeakPointer* wp;
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{
|
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if (wp == 0 || wp->pointer == 0) {
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return 0;}
|
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else {
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return (void*) wp->pointer;}}
|
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|
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void* _WeakPointer_Pointer( wp )
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WeakPointer* wp;
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{
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return (void*) GC_call_with_alloc_lock( PointerWithLock, wp );}
|
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|
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|
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typedef struct EqualClosure {
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WeakPointer* wp1;
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WeakPointer* wp2;
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} EqualClosure;
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static void* EqualWithLock( ec )
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EqualClosure* ec;
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{
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if (ec->wp1 == 0 || ec->wp2 == 0) {
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return (void*) (ec->wp1 == ec->wp2);}
|
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else {
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return (void*) (ec->wp1->pointer == ec->wp2->pointer);}}
|
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|
||||
|
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int _WeakPointer_Equal( wp1, wp2 )
|
||||
WeakPointer* wp1;
|
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WeakPointer* wp2;
|
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{
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EqualClosure ec;
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ec.wp1 = wp1;
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ec.wp2 = wp2;
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return (int) GC_call_with_alloc_lock( EqualWithLock, &ec );}
|
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|
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|
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int _WeakPointer_Hash( wp )
|
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WeakPointer* wp;
|
||||
{
|
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return (int) _WeakPointer_Pointer( wp );}
|
||||
|
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|
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/**************************************************************************
|
||||
|
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Implementations of the template class CleanUp from WeakPointer.h
|
||||
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***************************************************************************/
|
||||
|
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typedef struct Closure {
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void (*c) PROTO(( void* d, void* t ));
|
||||
ptrdiff_t t_offset;
|
||||
void* d;
|
||||
} Closure;
|
||||
|
||||
|
||||
static void _CleanUp_CallClosure( obj, data )
|
||||
void* obj;
|
||||
void* data;
|
||||
{
|
||||
Closure* closure = (Closure*) data;
|
||||
closure->c( closure->d, (char*) obj + closure->t_offset );}
|
||||
|
||||
|
||||
void _CleanUp_Set( t, c, d )
|
||||
void* t;
|
||||
void (*c) PROTO(( void* d, void* t ));
|
||||
void* d;
|
||||
{
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||||
void* base = GC_base( t );
|
||||
Descriptor* desc = DESCRIPTOR( t );
|
||||
|
||||
if (c == 0) {
|
||||
GC_REGISTER_FINALIZER_IGNORE_SELF( base, 0, 0, 0, 0 );
|
||||
desc->has_finalizer = 0;}
|
||||
else {
|
||||
Closure* closure = (Closure*) GC_MALLOC( sizeof( Closure ) );
|
||||
closure->c = c;
|
||||
closure->t_offset = (char*) t - (char*) base;
|
||||
closure->d = d;
|
||||
GC_REGISTER_FINALIZER_IGNORE_SELF( base, _CleanUp_CallClosure,
|
||||
closure, 0, 0 );
|
||||
desc->has_finalizer = 1;}}
|
||||
|
||||
|
||||
void _CleanUp_Call( t )
|
||||
void* t;
|
||||
{
|
||||
/* ? Aren't we supposed to deactivate weak pointers to t too?
|
||||
Why? */
|
||||
void* base = GC_base( t );
|
||||
void* d;
|
||||
GC_finalization_proc f;
|
||||
|
||||
GC_REGISTER_FINALIZER( base, 0, 0, &f, &d );
|
||||
f( base, d );}
|
||||
|
||||
|
||||
typedef struct QueueElem {
|
||||
void* o;
|
||||
GC_finalization_proc f;
|
||||
void* d;
|
||||
struct QueueElem* next;
|
||||
} QueueElem;
|
||||
|
||||
|
||||
void* _CleanUp_Queue_NewHead()
|
||||
{
|
||||
return GC_MALLOC( sizeof( QueueElem ) );}
|
||||
|
||||
|
||||
static void _CleanUp_Queue_Enqueue( obj, data )
|
||||
void* obj;
|
||||
void* data;
|
||||
{
|
||||
QueueElem* q = (QueueElem*) data;
|
||||
QueueElem* head = q->next;
|
||||
|
||||
q->o = obj;
|
||||
q->next = head->next;
|
||||
head->next = q;}
|
||||
|
||||
|
||||
void _CleanUp_Queue_Set( h, t )
|
||||
void* h;
|
||||
void* t;
|
||||
{
|
||||
QueueElem* head = (QueueElem*) h;
|
||||
void* base = GC_base( t );
|
||||
void* d;
|
||||
GC_finalization_proc f;
|
||||
QueueElem* q = (QueueElem*) GC_MALLOC( sizeof( QueueElem ) );
|
||||
|
||||
GC_REGISTER_FINALIZER( base, _CleanUp_Queue_Enqueue, q, &f, &d );
|
||||
q->f = f;
|
||||
q->d = d;
|
||||
q->next = head;}
|
||||
|
||||
|
||||
int _CleanUp_Queue_Call( h )
|
||||
void* h;
|
||||
{
|
||||
QueueElem* head = (QueueElem*) h;
|
||||
QueueElem* q = head->next;
|
||||
|
||||
if (q == 0) {
|
||||
return 0;}
|
||||
else {
|
||||
head->next = q->next;
|
||||
q->next = 0;
|
||||
if (q->f != 0) q->f( q->o, q->d );
|
||||
return 1;}}
|
||||
|
||||
|
||||
|
||||
Reference in New Issue
Block a user