mirror of
https://github.com/mozilla/gecko-dev.git
synced 2024-11-01 06:35:42 +00:00
291 lines
9.6 KiB
C++
291 lines
9.6 KiB
C++
#ifndef GC_CPP_H
|
|
#define GC_CPP_H
|
|
/****************************************************************************
|
|
Copyright (c) 1994 by Xerox Corporation. All rights reserved.
|
|
|
|
THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
|
|
OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
|
|
|
|
Permission is hereby granted to use or copy this program for any
|
|
purpose, provided the above notices are retained on all copies.
|
|
Permission to modify the code and to distribute modified code is
|
|
granted, provided the above notices are retained, and a notice that
|
|
the code was modified is included with the above copyright notice.
|
|
****************************************************************************
|
|
|
|
C++ Interface to the Boehm Collector
|
|
|
|
John R. Ellis and Jesse Hull
|
|
Last modified on Mon Jul 24 15:43:42 PDT 1995 by ellis
|
|
|
|
This interface provides access to the Boehm collector. It provides
|
|
basic facilities similar to those described in "Safe, Efficient
|
|
Garbage Collection for C++", by John R. Elis and David L. Detlefs
|
|
(ftp.parc.xerox.com:/pub/ellis/gc).
|
|
|
|
All heap-allocated objects are either "collectable" or
|
|
"uncollectable". Programs must explicitly delete uncollectable
|
|
objects, whereas the garbage collector will automatically delete
|
|
collectable objects when it discovers them to be inaccessible.
|
|
Collectable objects may freely point at uncollectable objects and vice
|
|
versa.
|
|
|
|
Objects allocated with the built-in "::operator new" are uncollectable.
|
|
|
|
Objects derived from class "gc" are collectable. For example:
|
|
|
|
class A: public gc {...};
|
|
A* a = new A; // a is collectable.
|
|
|
|
Collectable instances of non-class types can be allocated using the GC
|
|
placement:
|
|
|
|
typedef int A[ 10 ];
|
|
A* a = new (GC) A;
|
|
|
|
Uncollectable instances of classes derived from "gc" can be allocated
|
|
using the NoGC placement:
|
|
|
|
class A: public gc {...};
|
|
A* a = new (NoGC) A; // a is uncollectable.
|
|
|
|
Both uncollectable and collectable objects can be explicitly deleted
|
|
with "delete", which invokes an object's destructors and frees its
|
|
storage immediately.
|
|
|
|
A collectable object may have a clean-up function, which will be
|
|
invoked when the collector discovers the object to be inaccessible.
|
|
An object derived from "gc_cleanup" or containing a member derived
|
|
from "gc_cleanup" has a default clean-up function that invokes the
|
|
object's destructors. Explicit clean-up functions may be specified as
|
|
an additional placement argument:
|
|
|
|
A* a = ::new (GC, MyCleanup) A;
|
|
|
|
An object is considered "accessible" by the collector if it can be
|
|
reached by a path of pointers from static variables, automatic
|
|
variables of active functions, or from some object with clean-up
|
|
enabled; pointers from an object to itself are ignored.
|
|
|
|
Thus, if objects A and B both have clean-up functions, and A points at
|
|
B, B is considered accessible. After A's clean-up is invoked and its
|
|
storage released, B will then become inaccessible and will have its
|
|
clean-up invoked. If A points at B and B points to A, forming a
|
|
cycle, then that's considered a storage leak, and neither will be
|
|
collectable. See the interface gc.h for low-level facilities for
|
|
handling such cycles of objects with clean-up.
|
|
|
|
The collector cannot guarrantee that it will find all inaccessible
|
|
objects. In practice, it finds almost all of them.
|
|
|
|
|
|
Cautions:
|
|
|
|
1. Be sure the collector has been augmented with "make c++".
|
|
|
|
2. If your compiler supports the new "operator new[]" syntax, then
|
|
add -DOPERATOR_NEW_ARRAY to the Makefile.
|
|
|
|
If your compiler doesn't support "operator new[]", beware that an
|
|
array of type T, where T is derived from "gc", may or may not be
|
|
allocated as a collectable object (it depends on the compiler). Use
|
|
the explicit GC placement to make the array collectable. For example:
|
|
|
|
class A: public gc {...};
|
|
A* a1 = new A[ 10 ]; // collectable or uncollectable?
|
|
A* a2 = new (GC) A[ 10 ]; // collectable
|
|
|
|
3. The destructors of collectable arrays of objects derived from
|
|
"gc_cleanup" will not be invoked properly. For example:
|
|
|
|
class A: public gc_cleanup {...};
|
|
A* a = new (GC) A[ 10 ]; // destructors not invoked correctly
|
|
|
|
Typically, only the destructor for the first element of the array will
|
|
be invoked when the array is garbage-collected. To get all the
|
|
destructors of any array executed, you must supply an explicit
|
|
clean-up function:
|
|
|
|
A* a = new (GC, MyCleanUp) A[ 10 ];
|
|
|
|
(Implementing clean-up of arrays correctly, portably, and in a way
|
|
that preserves the correct exception semantics requires a language
|
|
extension, e.g. the "gc" keyword.)
|
|
|
|
4. Compiler bugs:
|
|
|
|
* Solaris 2's CC (SC3.0) doesn't implement t->~T() correctly, so the
|
|
destructors of classes derived from gc_cleanup won't be invoked.
|
|
You'll have to explicitly register a clean-up function with
|
|
new-placement syntax.
|
|
|
|
* Evidently cfront 3.0 does not allow destructors to be explicitly
|
|
invoked using the ANSI-conforming syntax t->~T(). If you're using
|
|
cfront 3.0, you'll have to comment out the class gc_cleanup, which
|
|
uses explicit invocation.
|
|
|
|
****************************************************************************/
|
|
|
|
#include "gc.h"
|
|
|
|
#ifndef THINK_CPLUS
|
|
#define _cdecl
|
|
#endif
|
|
|
|
#if ! defined( OPERATOR_NEW_ARRAY ) \
|
|
&& (__BORLANDC__ >= 0x450 || (__GNUC__ >= 2 && __GNUC_MINOR__ >= 6) \
|
|
|| __WATCOMC__ >= 1050)
|
|
# define OPERATOR_NEW_ARRAY
|
|
#endif
|
|
|
|
enum GCPlacement {GC, NoGC, PointerFreeGC};
|
|
|
|
class gc {public:
|
|
inline void* operator new( size_t size );
|
|
inline void* operator new( size_t size, GCPlacement gcp );
|
|
inline void operator delete( void* obj );
|
|
|
|
#ifdef OPERATOR_NEW_ARRAY
|
|
inline void* operator new[]( size_t size );
|
|
inline void* operator new[]( size_t size, GCPlacement gcp );
|
|
inline void operator delete[]( void* obj );
|
|
#endif /* OPERATOR_NEW_ARRAY */
|
|
};
|
|
/*
|
|
Instances of classes derived from "gc" will be allocated in the
|
|
collected heap by default, unless an explicit NoGC placement is
|
|
specified. */
|
|
|
|
class gc_cleanup: virtual public gc {public:
|
|
inline gc_cleanup();
|
|
inline virtual ~gc_cleanup();
|
|
private:
|
|
inline static void _cdecl cleanup( void* obj, void* clientData );};
|
|
/*
|
|
Instances of classes derived from "gc_cleanup" will be allocated
|
|
in the collected heap by default. When the collector discovers an
|
|
inaccessible object derived from "gc_cleanup" or containing a
|
|
member derived from "gc_cleanup", its destructors will be
|
|
invoked. */
|
|
|
|
extern "C" {typedef void (*GCCleanUpFunc)( void* obj, void* clientData );}
|
|
|
|
inline void* operator new(
|
|
size_t size,
|
|
GCPlacement gcp,
|
|
GCCleanUpFunc cleanup = 0,
|
|
void* clientData = 0 );
|
|
/*
|
|
Allocates a collectable or uncollected object, according to the
|
|
value of "gcp".
|
|
|
|
For collectable objects, if "cleanup" is non-null, then when the
|
|
allocated object "obj" becomes inaccessible, the collector will
|
|
invoke the function "cleanup( obj, clientData )" but will not
|
|
invoke the object's destructors. It is an error to explicitly
|
|
delete an object allocated with a non-null "cleanup".
|
|
|
|
It is an error to specify a non-null "cleanup" with NoGC or for
|
|
classes derived from "gc_cleanup" or containing members derived
|
|
from "gc_cleanup". */
|
|
|
|
#ifdef OPERATOR_NEW_ARRAY
|
|
|
|
inline void* operator new[](
|
|
size_t size,
|
|
GCPlacement gcp,
|
|
GCCleanUpFunc cleanup = 0,
|
|
void* clientData = 0 );
|
|
/*
|
|
The operator new for arrays, identical to the above. */
|
|
|
|
#endif /* OPERATOR_NEW_ARRAY */
|
|
|
|
/****************************************************************************
|
|
|
|
Inline implementation
|
|
|
|
****************************************************************************/
|
|
|
|
inline void* gc::operator new( size_t size ) {
|
|
return GC_MALLOC( size );}
|
|
|
|
inline void* gc::operator new( size_t size, GCPlacement gcp ) {
|
|
if (gcp == GC)
|
|
return GC_MALLOC( size );
|
|
else if (gcp == PointerFreeGC)
|
|
return GC_MALLOC_ATOMIC( size );
|
|
else
|
|
return GC_MALLOC_UNCOLLECTABLE( size );}
|
|
|
|
inline void gc::operator delete( void* obj ) {
|
|
GC_FREE( obj );}
|
|
|
|
|
|
#ifdef OPERATOR_NEW_ARRAY
|
|
|
|
inline void* gc::operator new[]( size_t size ) {
|
|
return gc::operator new( size );}
|
|
|
|
inline void* gc::operator new[]( size_t size, GCPlacement gcp ) {
|
|
return gc::operator new( size, gcp );}
|
|
|
|
inline void gc::operator delete[]( void* obj ) {
|
|
gc::operator delete( obj );}
|
|
|
|
#endif /* OPERATOR_NEW_ARRAY */
|
|
|
|
|
|
inline gc_cleanup::~gc_cleanup() {
|
|
GC_REGISTER_FINALIZER_IGNORE_SELF( GC_base(this), 0, 0, 0, 0 );}
|
|
|
|
inline void gc_cleanup::cleanup( void* obj, void* displ ) {
|
|
((gc_cleanup*) ((char*) obj + (ptrdiff_t) displ))->~gc_cleanup();}
|
|
|
|
inline gc_cleanup::gc_cleanup() {
|
|
GC_finalization_proc oldProc;
|
|
void* oldData;
|
|
void* base = GC_base( (void *) this );
|
|
if (0 == base) return;
|
|
GC_REGISTER_FINALIZER_IGNORE_SELF(
|
|
base, cleanup, (void*) ((char*) this - (char*) base),
|
|
&oldProc, &oldData );
|
|
if (0 != oldProc) {
|
|
GC_REGISTER_FINALIZER_IGNORE_SELF( base, oldProc, oldData, 0, 0 );}}
|
|
|
|
inline void* operator new(
|
|
size_t size,
|
|
GCPlacement gcp,
|
|
GCCleanUpFunc cleanup,
|
|
void* clientData )
|
|
{
|
|
void* obj;
|
|
|
|
if (gcp == GC) {
|
|
obj = GC_MALLOC( size );
|
|
if (cleanup != 0)
|
|
GC_REGISTER_FINALIZER_IGNORE_SELF(
|
|
obj, cleanup, clientData, 0, 0 );}
|
|
else if (gcp == PointerFreeGC) {
|
|
obj = GC_MALLOC_ATOMIC( size );}
|
|
else {
|
|
obj = GC_MALLOC_UNCOLLECTABLE( size );};
|
|
return obj;}
|
|
|
|
|
|
#ifdef OPERATOR_NEW_ARRAY
|
|
|
|
inline void* operator new[](
|
|
size_t size,
|
|
GCPlacement gcp,
|
|
GCCleanUpFunc cleanup,
|
|
void* clientData )
|
|
{
|
|
return ::operator new( size, gcp, cleanup, clientData );}
|
|
|
|
#endif /* OPERATOR_NEW_ARRAY */
|
|
|
|
|
|
#endif /* GC_CPP_H */
|
|
|