/* * Copyright (c) 1991-1994 by Xerox Corporation. All rights reserved. * Copyright (c) 2001 by Hewlett-Packard Company. 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. * */ /* * This contains interfaces to the GC marker that are likely to be useful to * clients that provide detailed heap layout information to the collector. * This interface should not be used by normal C or C++ clients. * It will be useful to runtimes for other languages. * * This is an experts-only interface! There are many ways to break the * collector in subtle ways by using this functionality. */ #ifndef GC_MARK_H # define GC_MARK_H # ifndef GC_H # include "gc.h" # endif /* A client supplied mark procedure. Returns new mark stack pointer. */ /* Primary effect should be to push new entries on the mark stack. */ /* Mark stack pointer values are passed and returned explicitly. */ /* Global variables decribing mark stack are not necessarily valid. */ /* (This usually saves a few cycles by keeping things in registers.) */ /* Assumed to scan about GC_PROC_BYTES on average. If it needs to do */ /* much more work than that, it should do it in smaller pieces by */ /* pushing itself back on the mark stack. */ /* Note that it should always do some work (defined as marking some */ /* objects) before pushing more than one entry on the mark stack. */ /* This is required to ensure termination in the event of mark stack */ /* overflows. */ /* This procedure is always called with at least one empty entry on the */ /* mark stack. */ /* Currently we require that mark procedures look for pointers in a */ /* subset of the places the conservative marker would. It must be safe */ /* to invoke the normal mark procedure instead. */ /* WARNING: Such a mark procedure may be invoked on an unused object */ /* residing on a free list. Such objects are cleared, except for a */ /* free list link field in the first word. Thus mark procedures may */ /* not count on the presence of a type descriptor, and must handle this */ /* case correctly somehow. */ # define GC_PROC_BYTES 100 struct GC_ms_entry; typedef struct GC_ms_entry * (*GC_mark_proc) GC_PROTO(( GC_word * addr, struct GC_ms_entry * mark_stack_ptr, struct GC_ms_entry * mark_stack_limit, GC_word env)); # define GC_LOG_MAX_MARK_PROCS 6 # define GC_MAX_MARK_PROCS (1 << GC_LOG_MAX_MARK_PROCS) /* In a few cases it's necessary to assign statically known indices to */ /* certain mark procs. Thus we reserve a few for well known clients. */ /* (This is necessary if mark descriptors are compiler generated.) */ #define GC_RESERVED_MARK_PROCS 8 # define GC_GCJ_RESERVED_MARK_PROC_INDEX 0 /* Object descriptors on mark stack or in objects. Low order two */ /* bits are tags distinguishing among the following 4 possibilities */ /* for the high order 30 bits. */ #define GC_DS_TAG_BITS 2 #define GC_DS_TAGS ((1 << GC_DS_TAG_BITS) - 1) #define GC_DS_LENGTH 0 /* The entire word is a length in bytes that */ /* must be a multiple of 4. */ #define GC_DS_BITMAP 1 /* 30 (62) bits are a bitmap describing pointer */ /* fields. The msb is 1 iff the first word */ /* is a pointer. */ /* (This unconventional ordering sometimes */ /* makes the marker slightly faster.) */ /* Zeroes indicate definite nonpointers. Ones */ /* indicate possible pointers. */ /* Only usable if pointers are word aligned. */ #define GC_DS_PROC 2 /* The objects referenced by this object can be */ /* pushed on the mark stack by invoking */ /* PROC(descr). ENV(descr) is passed as the */ /* last argument. */ # define GC_MAKE_PROC(proc_index, env) \ (((((env) << GC_LOG_MAX_MARK_PROCS) \ | (proc_index)) << GC_DS_TAG_BITS) | GC_DS_PROC) #define GC_DS_PER_OBJECT 3 /* The real descriptor is at the */ /* byte displacement from the beginning of the */ /* object given by descr & ~DS_TAGS */ /* If the descriptor is negative, the real */ /* descriptor is at (*<object_start>) - */ /* (descr & ~DS_TAGS) - GC_INDIR_PER_OBJ_BIAS */ /* The latter alternative can be used if each */ /* object contains a type descriptor in the */ /* first word. */ /* Note that in multithreaded environments */ /* per object descriptors maust be located in */ /* either the first two or last two words of */ /* the object, since only those are guaranteed */ /* to be cleared while the allocation lock is */ /* held. */ #define GC_INDIR_PER_OBJ_BIAS 0x10 extern GC_PTR GC_least_plausible_heap_addr; extern GC_PTR GC_greatest_plausible_heap_addr; /* Bounds on the heap. Guaranteed valid */ /* Likely to include future heap expansion. */ /* Handle nested references in a custom mark procedure. */ /* Check if obj is a valid object. If so, ensure that it is marked. */ /* If it was not previously marked, push its contents onto the mark */ /* stack for future scanning. The object will then be scanned using */ /* its mark descriptor. */ /* Returns the new mark stack pointer. */ /* Handles mark stack overflows correctly. */ /* Since this marks first, it makes progress even if there are mark */ /* stack overflows. */ /* Src is the address of the pointer to obj, which is used only */ /* for back pointer-based heap debugging. */ /* It is strongly recommended that most objects be handled without mark */ /* procedures, e.g. with bitmap descriptors, and that mark procedures */ /* be reserved for exceptional cases. That will ensure that */ /* performance of this call is not extremely performance critical. */ /* (Otherwise we would need to inline GC_mark_and_push completely, */ /* which would tie the client code to a fixed collector version.) */ /* Note that mark procedures should explicitly call FIXUP_POINTER() */ /* if required. */ struct GC_ms_entry *GC_mark_and_push GC_PROTO((GC_PTR obj, struct GC_ms_entry * mark_stack_ptr, struct GC_ms_entry * mark_stack_limit, GC_PTR *src)); #define GC_MARK_AND_PUSH(obj, msp, lim, src) \ (((GC_word)obj >= (GC_word)GC_least_plausible_heap_addr && \ (GC_word)obj <= (GC_word)GC_greatest_plausible_heap_addr)? \ GC_mark_and_push(obj, msp, lim, src) : \ msp) extern size_t GC_debug_header_size; /* The size of the header added to objects allocated through */ /* the GC_debug routines. */ /* Defined as a variable so that client mark procedures don't */ /* need to be recompiled for collector version changes. */ #define GC_USR_PTR_FROM_BASE(p) ((GC_PTR)((char *)(p) + GC_debug_header_size)) /* And some routines to support creation of new "kinds", e.g. with */ /* custom mark procedures, by language runtimes. */ /* The _inner versions assume the caller holds the allocation lock. */ /* Return a new free list array. */ void ** GC_new_free_list GC_PROTO((void)); void ** GC_new_free_list_inner GC_PROTO((void)); /* Return a new kind, as specified. */ int GC_new_kind GC_PROTO((void **free_list, GC_word mark_descriptor_template, int add_size_to_descriptor, int clear_new_objects)); /* The last two parameters must be zero or one. */ int GC_new_kind_inner GC_PROTO((void **free_list, GC_word mark_descriptor_template, int add_size_to_descriptor, int clear_new_objects)); /* Return a new mark procedure identifier, suitable for use as */ /* the first argument in GC_MAKE_PROC. */ int GC_new_proc GC_PROTO((GC_mark_proc)); int GC_new_proc_inner GC_PROTO((GC_mark_proc)); /* Allocate an object of a given kind. Note that in multithreaded */ /* contexts, this is usually unsafe for kinds that have the descriptor */ /* in the object itself, since there is otherwise a window in which */ /* the descriptor is not correct. Even in the single-threaded case, */ /* we need to be sure that cleared objects on a free list don't */ /* cause a GC crash if they are accidentally traced. */ /* ptr_t */char * GC_generic_malloc GC_PROTO((GC_word lb, int k)); /* FIXME - Should return void *, but that requires other changes. */ typedef void (*GC_describe_type_fn) GC_PROTO((void *p, char *out_buf)); /* A procedure which */ /* produces a human-readable */ /* description of the "type" of object */ /* p into the buffer out_buf of length */ /* GC_TYPE_DESCR_LEN. This is used by */ /* the debug support when printing */ /* objects. */ /* These functions should be as robust */ /* as possible, though we do avoid */ /* invoking them on objects on the */ /* global free list. */ # define GC_TYPE_DESCR_LEN 40 void GC_register_describe_type_fn GC_PROTO((int kind, GC_describe_type_fn knd)); /* Register a describe_type function */ /* to be used when printing objects */ /* of a particular kind. */ #endif /* GC_MARK_H */