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mark.c
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/*
* Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
* Copyright (c) 1991-1995 by Xerox Corporation. All rights reserved.
* Copyright (c) 2000 by Hewlett-Packard Company. All rights reserved.
* Copyright (c) 2008-2020 Ivan Maidanski
*
* 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.
*
*/
#if defined(__MINGW32__) && !defined(__MINGW_EXCPT_DEFINE_PSDK) \
&& defined(__i386__) /* cannot use macros from gcconfig.h */
/* Otherwise EXCEPTION_REGISTRATION type declaration from winnt.h */
/* might be used. That declaration has "handler" callback with NTAPI */
/* attribute. The proper type (with "handler" field compatible with */
/* GC mark_ex_handler) is declared in excpt.h. The given macro is */
/* defined before any system header include. */
# define __MINGW_EXCPT_DEFINE_PSDK 1
#endif
#include "private/gc_pmark.h"
#include <stdio.h>
#if defined(MSWIN32) && defined(__GNUC__)
# include <excpt.h>
#endif
/* Make arguments appear live to compiler. Put here to minimize the */
/* risk of inlining. Used to minimize junk left in registers. */
GC_ATTR_NOINLINE
void GC_noop6(word arg1 GC_ATTR_UNUSED, word arg2 GC_ATTR_UNUSED,
word arg3 GC_ATTR_UNUSED, word arg4 GC_ATTR_UNUSED,
word arg5 GC_ATTR_UNUSED, word arg6 GC_ATTR_UNUSED)
{
/* Avoid GC_noop6 calls to be optimized away. */
# if defined(AO_HAVE_compiler_barrier) && !defined(BASE_ATOMIC_OPS_EMULATED)
AO_compiler_barrier(); /* to serve as a special side-effect */
# else
GC_noop1(0);
# endif
}
volatile word GC_noop_sink;
/* Single argument version, robust against whole program analysis. */
GC_ATTR_NO_SANITIZE_THREAD
GC_API void GC_CALL GC_noop1(word x)
{
GC_noop_sink = x;
}
/* Initialize GC_obj_kinds properly and standard free lists properly. */
/* This must be done statically since they may be accessed before */
/* GC_init is called. */
/* It's done here, since we need to deal with mark descriptors. */
GC_INNER struct obj_kind GC_obj_kinds[MAXOBJKINDS] = {
/* PTRFREE */ { &GC_aobjfreelist[0], 0 /* filled in dynamically */,
/* 0 | */ GC_DS_LENGTH, FALSE, FALSE
/*, */ OK_DISCLAIM_INITZ },
/* NORMAL */ { &GC_objfreelist[0], 0,
/* 0 | */ GC_DS_LENGTH,
/* adjusted in GC_init for EXTRA_BYTES */
TRUE /* add length to descr */, TRUE
/*, */ OK_DISCLAIM_INITZ },
/* UNCOLLECTABLE */
{ &GC_uobjfreelist[0], 0,
/* 0 | */ GC_DS_LENGTH, TRUE /* add length to descr */, TRUE
/*, */ OK_DISCLAIM_INITZ },
# ifdef GC_ATOMIC_UNCOLLECTABLE
{ &GC_auobjfreelist[0], 0,
/* 0 | */ GC_DS_LENGTH, FALSE /* add length to descr */, FALSE
/*, */ OK_DISCLAIM_INITZ },
# endif
};
# ifndef INITIAL_MARK_STACK_SIZE
# define INITIAL_MARK_STACK_SIZE (1*HBLKSIZE)
/* INITIAL_MARK_STACK_SIZE * sizeof(mse) should be a */
/* multiple of HBLKSIZE. */
/* The incremental collector actually likes a larger */
/* size, since it wants to push all marked dirty */
/* objects before marking anything new. Currently we */
/* let it grow dynamically. */
# endif
#if !defined(GC_DISABLE_INCREMENTAL)
STATIC word GC_n_rescuing_pages = 0;
/* Number of dirty pages we marked from */
/* excludes ptrfree pages, etc. */
/* Used for logging only. */
#endif
#ifdef PARALLEL_MARK
GC_INNER GC_bool GC_parallel_mark_disabled = FALSE;
#endif
/* Is a collection in progress? Note that this can return true in the */
/* non-incremental case, if a collection has been abandoned and the */
/* mark state is now MS_INVALID. */
GC_INNER GC_bool GC_collection_in_progress(void)
{
return(GC_mark_state != MS_NONE);
}
/* Clear all mark bits in the header. */
GC_INNER void GC_clear_hdr_marks(hdr *hhdr)
{
size_t last_bit;
# ifdef AO_HAVE_load
/* Atomic access is used to avoid racing with GC_realloc. */
last_bit = FINAL_MARK_BIT((size_t)AO_load((volatile AO_t *)&hhdr->hb_sz));
# else
/* No race as GC_realloc holds the lock while updating hb_sz. */
last_bit = FINAL_MARK_BIT((size_t)hhdr->hb_sz);
# endif
BZERO(hhdr -> hb_marks, sizeof(hhdr->hb_marks));
set_mark_bit_from_hdr(hhdr, last_bit);
hhdr -> hb_n_marks = 0;
}
/* Set all mark bits in the header. Used for uncollectible blocks. */
GC_INNER void GC_set_hdr_marks(hdr *hhdr)
{
unsigned i;
size_t sz = (size_t)hhdr->hb_sz;
unsigned n_marks = (unsigned)FINAL_MARK_BIT(sz);
# ifdef USE_MARK_BYTES
for (i = 0; i <= n_marks; i += (unsigned)MARK_BIT_OFFSET(sz)) {
hhdr -> hb_marks[i] = 1;
}
# else
for (i = 0; i < divWORDSZ(n_marks + WORDSZ); ++i) {
hhdr -> hb_marks[i] = GC_WORD_MAX;
}
# endif
# ifdef MARK_BIT_PER_OBJ
hhdr -> hb_n_marks = n_marks;
# else
hhdr -> hb_n_marks = HBLK_OBJS(sz);
# endif
}
/* Clear all mark bits associated with block h. */
static void clear_marks_for_block(struct hblk *h, word dummy GC_ATTR_UNUSED)
{
hdr * hhdr = HDR(h);
if (IS_UNCOLLECTABLE(hhdr -> hb_obj_kind)) return;
/* Mark bit for these is cleared only once the object is */
/* explicitly deallocated. This either frees the block, or */
/* the bit is cleared once the object is on the free list. */
GC_clear_hdr_marks(hhdr);
}
/* Slow but general routines for setting/clearing/asking about mark bits. */
GC_API void GC_CALL GC_set_mark_bit(const void *p)
{
struct hblk *h = HBLKPTR(p);
hdr * hhdr = HDR(h);
word bit_no = MARK_BIT_NO((ptr_t)p - (ptr_t)h, hhdr -> hb_sz);
if (!mark_bit_from_hdr(hhdr, bit_no)) {
set_mark_bit_from_hdr(hhdr, bit_no);
++hhdr -> hb_n_marks;
}
}
GC_API void GC_CALL GC_clear_mark_bit(const void *p)
{
struct hblk *h = HBLKPTR(p);
hdr * hhdr = HDR(h);
word bit_no = MARK_BIT_NO((ptr_t)p - (ptr_t)h, hhdr -> hb_sz);
if (mark_bit_from_hdr(hhdr, bit_no)) {
size_t n_marks = hhdr -> hb_n_marks;
GC_ASSERT(n_marks != 0);
clear_mark_bit_from_hdr(hhdr, bit_no);
n_marks--;
# ifdef PARALLEL_MARK
if (n_marks != 0 || !GC_parallel)
hhdr -> hb_n_marks = n_marks;
/* Don't decrement to zero. The counts are approximate due to */
/* concurrency issues, but we need to ensure that a count of */
/* zero implies an empty block. */
# else
hhdr -> hb_n_marks = n_marks;
# endif
}
}
GC_API int GC_CALL GC_is_marked(const void *p)
{
struct hblk *h = HBLKPTR(p);
hdr * hhdr = HDR(h);
word bit_no = MARK_BIT_NO((ptr_t)p - (ptr_t)h, hhdr -> hb_sz);
return (int)mark_bit_from_hdr(hhdr, bit_no); /* 0 or 1 */
}
/* Clear mark bits in all allocated heap blocks. This invalidates the */
/* marker invariant, and sets GC_mark_state to reflect this. (This */
/* implicitly starts marking to reestablish the invariant.) */
GC_INNER void GC_clear_marks(void)
{
GC_apply_to_all_blocks(clear_marks_for_block, (word)0);
GC_objects_are_marked = FALSE;
GC_mark_state = MS_INVALID;
GC_scan_ptr = NULL;
}
/* Initiate a garbage collection. Initiates a full collection if the */
/* mark state is invalid. */
GC_INNER void GC_initiate_gc(void)
{
GC_ASSERT(I_HOLD_LOCK());
# ifndef GC_DISABLE_INCREMENTAL
if (GC_incremental) {
# ifdef CHECKSUMS
GC_read_dirty(FALSE);
GC_check_dirty();
# else
GC_read_dirty(GC_mark_state == MS_INVALID);
# endif
}
GC_n_rescuing_pages = 0;
# endif
if (GC_mark_state == MS_NONE) {
GC_mark_state = MS_PUSH_RESCUERS;
} else if (GC_mark_state != MS_INVALID) {
ABORT("Unexpected state");
} /* Else this is really a full collection, and mark bits are invalid. */
GC_scan_ptr = NULL;
}
#ifdef PARALLEL_MARK
STATIC void GC_do_parallel_mark(void); /* Initiate parallel marking. */
#endif /* PARALLEL_MARK */
#ifdef GC_DISABLE_INCREMENTAL
# define GC_push_next_marked_dirty(h) GC_push_next_marked(h)
#else
STATIC struct hblk * GC_push_next_marked_dirty(struct hblk *h);
/* Invoke GC_push_marked on next dirty block above h. */
/* Return a pointer just past the end of this block. */
#endif /* !GC_DISABLE_INCREMENTAL */
STATIC struct hblk * GC_push_next_marked(struct hblk *h);
/* Ditto, but also mark from clean pages. */
STATIC struct hblk * GC_push_next_marked_uncollectable(struct hblk *h);
/* Ditto, but mark only from uncollectible pages. */
static void alloc_mark_stack(size_t);
/* Perform a small amount of marking. */
/* We try to touch roughly a page of memory. */
/* Return TRUE if we just finished a mark phase. */
/* Cold_gc_frame is an address inside a GC frame that */
/* remains valid until all marking is complete. */
/* A zero value indicates that it's OK to miss some */
/* register values. */
/* We hold the allocation lock. In the case of */
/* incremental collection, the world may not be stopped.*/
#ifdef WRAP_MARK_SOME
/* For win32, this is called after we establish a structured */
/* exception handler, in case Windows unmaps one of our root */
/* segments. See below. In either case, we acquire the */
/* allocator lock long before we get here. */
STATIC GC_bool GC_mark_some_inner(ptr_t cold_gc_frame)
#else
GC_INNER GC_bool GC_mark_some(ptr_t cold_gc_frame)
#endif
{
switch(GC_mark_state) {
case MS_NONE:
break;
case MS_PUSH_RESCUERS:
if ((word)GC_mark_stack_top
>= (word)(GC_mark_stack_limit - INITIAL_MARK_STACK_SIZE/2)) {
/* Go ahead and mark, even though that might cause us to */
/* see more marked dirty objects later on. Avoid this */
/* in the future. */
GC_mark_stack_too_small = TRUE;
MARK_FROM_MARK_STACK();
break;
} else {
GC_scan_ptr = GC_push_next_marked_dirty(GC_scan_ptr);
if (NULL == GC_scan_ptr) {
# if !defined(GC_DISABLE_INCREMENTAL)
GC_COND_LOG_PRINTF("Marked from %lu dirty pages\n",
(unsigned long)GC_n_rescuing_pages);
# endif
GC_push_roots(FALSE, cold_gc_frame);
GC_objects_are_marked = TRUE;
if (GC_mark_state != MS_INVALID) {
GC_mark_state = MS_ROOTS_PUSHED;
}
}
}
break;
case MS_PUSH_UNCOLLECTABLE:
if ((word)GC_mark_stack_top
>= (word)(GC_mark_stack + GC_mark_stack_size/4)) {
# ifdef PARALLEL_MARK
/* Avoid this, since we don't parallelize the marker */
/* here. */
if (GC_parallel) GC_mark_stack_too_small = TRUE;
# endif
MARK_FROM_MARK_STACK();
break;
} else {
GC_scan_ptr = GC_push_next_marked_uncollectable(GC_scan_ptr);
if (NULL == GC_scan_ptr) {
GC_push_roots(TRUE, cold_gc_frame);
GC_objects_are_marked = TRUE;
if (GC_mark_state != MS_INVALID) {
GC_mark_state = MS_ROOTS_PUSHED;
}
}
}
break;
case MS_ROOTS_PUSHED:
# ifdef PARALLEL_MARK
/* Eventually, incremental marking should run */
/* asynchronously in multiple threads, without grabbing */
/* the allocation lock. */
/* For now, parallel marker is disabled if there is */
/* a chance that marking could be interrupted by */
/* a client-supplied time limit or custom stop function. */
if (GC_parallel && !GC_parallel_mark_disabled) {
GC_do_parallel_mark();
GC_ASSERT((word)GC_mark_stack_top < (word)GC_first_nonempty);
GC_mark_stack_top = GC_mark_stack - 1;
if (GC_mark_stack_too_small) {
alloc_mark_stack(2*GC_mark_stack_size);
}
if (GC_mark_state == MS_ROOTS_PUSHED) {
GC_mark_state = MS_NONE;
return(TRUE);
}
break;
}
# endif
if ((word)GC_mark_stack_top >= (word)GC_mark_stack) {
MARK_FROM_MARK_STACK();
break;
} else {
GC_mark_state = MS_NONE;
if (GC_mark_stack_too_small) {
alloc_mark_stack(2*GC_mark_stack_size);
}
return(TRUE);
}
case MS_INVALID:
case MS_PARTIALLY_INVALID:
if (!GC_objects_are_marked) {
GC_mark_state = MS_PUSH_UNCOLLECTABLE;
break;
}
if ((word)GC_mark_stack_top >= (word)GC_mark_stack) {
MARK_FROM_MARK_STACK();
break;
}
if (NULL == GC_scan_ptr && GC_mark_state == MS_INVALID) {
/* About to start a heap scan for marked objects. */
/* Mark stack is empty. OK to reallocate. */
if (GC_mark_stack_too_small) {
alloc_mark_stack(2*GC_mark_stack_size);
}
GC_mark_state = MS_PARTIALLY_INVALID;
}
GC_scan_ptr = GC_push_next_marked(GC_scan_ptr);
if (NULL == GC_scan_ptr && GC_mark_state == MS_PARTIALLY_INVALID) {
GC_push_roots(TRUE, cold_gc_frame);
GC_objects_are_marked = TRUE;
if (GC_mark_state != MS_INVALID) {
GC_mark_state = MS_ROOTS_PUSHED;
}
}
break;
default:
ABORT("GC_mark_some: bad state");
}
return(FALSE);
}
#ifdef WRAP_MARK_SOME
# if (defined(MSWIN32) || defined(MSWINCE)) && defined(__GNUC__)
typedef struct {
EXCEPTION_REGISTRATION ex_reg;
void *alt_path;
} ext_ex_regn;
static EXCEPTION_DISPOSITION mark_ex_handler(
struct _EXCEPTION_RECORD *ex_rec,
void *est_frame,
struct _CONTEXT *context,
void *disp_ctxt GC_ATTR_UNUSED)
{
if (ex_rec->ExceptionCode == STATUS_ACCESS_VIOLATION) {
ext_ex_regn *xer = (ext_ex_regn *)est_frame;
/* Unwind from the inner function assuming the standard */
/* function prologue. */
/* Assumes code has not been compiled with */
/* -fomit-frame-pointer. */
context->Esp = context->Ebp;
context->Ebp = *((DWORD *)context->Esp);
context->Esp = context->Esp - 8;
/* Resume execution at the "real" handler within the */
/* wrapper function. */
context->Eip = (DWORD )(xer->alt_path);
return ExceptionContinueExecution;
} else {
return ExceptionContinueSearch;
}
}
# endif /* __GNUC__ && MSWIN32 */
GC_INNER GC_bool GC_mark_some(ptr_t cold_gc_frame)
{
GC_bool ret_val;
# if defined(MSWIN32) || defined(MSWINCE)
# ifndef __GNUC__
/* Windows 98 appears to asynchronously create and remove */
/* writable memory mappings, for reasons we haven't yet */
/* understood. Since we look for writable regions to */
/* determine the root set, we may try to mark from an */
/* address range that disappeared since we started the */
/* collection. Thus we have to recover from faults here. */
/* This code does not appear to be necessary for Windows */
/* 95/NT/2000+. Note that this code should never generate */
/* an incremental GC write fault. */
/* This code seems to be necessary for WinCE (at least in */
/* the case we'd decide to add MEM_PRIVATE sections to */
/* data roots in GC_register_dynamic_libraries()). */
/* It's conceivable that this is the same issue with */
/* terminating threads that we see with Linux and */
/* USE_PROC_FOR_LIBRARIES. */
__try {
ret_val = GC_mark_some_inner(cold_gc_frame);
} __except (GetExceptionCode() == EXCEPTION_ACCESS_VIOLATION ?
EXCEPTION_EXECUTE_HANDLER : EXCEPTION_CONTINUE_SEARCH) {
goto handle_ex;
}
# if defined(GC_WIN32_THREADS) && !defined(GC_PTHREADS)
/* With DllMain-based thread tracking, a thread may have */
/* started while we were marking. This is logically equivalent */
/* to the exception case; our results are invalid and we have */
/* to start over. This cannot be prevented since we can't */
/* block in DllMain. */
if (GC_started_thread_while_stopped())
goto handle_thr_start;
# endif
rm_handler:
return ret_val;
# else /* __GNUC__ */
/* Manually install an exception handler since GCC does */
/* not yet support Structured Exception Handling (SEH) on */
/* Win32. */
ext_ex_regn er;
# if GC_GNUC_PREREQ(4, 7) || GC_CLANG_PREREQ(3, 3)
# pragma GCC diagnostic push
/* Suppress "taking the address of label is non-standard" warning. */
# if defined(__clang__) || GC_GNUC_PREREQ(6, 4)
# pragma GCC diagnostic ignored "-Wpedantic"
# else
/* GCC before ~4.8 does not accept "-Wpedantic" quietly. */
# pragma GCC diagnostic ignored "-pedantic"
# endif
er.alt_path = &&handle_ex;
# pragma GCC diagnostic pop
# elif !defined(CPPCHECK) /* pragma diagnostic is not supported */
er.alt_path = &&handle_ex;
# endif
er.ex_reg.handler = mark_ex_handler;
__asm__ __volatile__ ("movl %%fs:0, %0" : "=r" (er.ex_reg.prev));
__asm__ __volatile__ ("movl %0, %%fs:0" : : "r" (&er));
ret_val = GC_mark_some_inner(cold_gc_frame);
/* Prevent GCC from considering the following code unreachable */
/* and thus eliminating it. */
if (er.alt_path == 0)
goto handle_ex;
# if defined(GC_WIN32_THREADS) && !defined(GC_PTHREADS)
if (GC_started_thread_while_stopped())
goto handle_thr_start;
# endif
rm_handler:
/* Uninstall the exception handler. */
__asm__ __volatile__ ("mov %0, %%fs:0" : : "r" (er.ex_reg.prev));
return ret_val;
# endif /* __GNUC__ */
# else /* !MSWIN32 */
/* Here we are handling the case in which /proc is used for root */
/* finding, and we have threads. We may find a stack for a */
/* thread that is in the process of exiting, and disappears */
/* while we are marking it. This seems extremely difficult to */
/* avoid otherwise. */
# ifndef DEFAULT_VDB
if (GC_auto_incremental) {
WARN("Incremental GC incompatible with /proc roots\n", 0);
/* I'm not sure if this could still work ... */
}
# endif
GC_setup_temporary_fault_handler();
if(SETJMP(GC_jmp_buf) != 0) goto handle_ex;
ret_val = GC_mark_some_inner(cold_gc_frame);
rm_handler:
GC_reset_fault_handler();
return ret_val;
# endif /* !MSWIN32 */
handle_ex:
/* Exception handler starts here for all cases. */
{
static word warned_gc_no;
/* Warn about it at most once per collection. */
if (warned_gc_no != GC_gc_no) {
WARN("Caught ACCESS_VIOLATION in marker;"
" memory mapping disappeared\n", 0);
warned_gc_no = GC_gc_no;
}
}
# if (defined(MSWIN32) || defined(MSWINCE)) && defined(GC_WIN32_THREADS) \
&& !defined(GC_PTHREADS)
handle_thr_start:
# endif
/* We have bad roots on the stack. Discard mark stack. */
/* Rescan from marked objects. Redetermine roots. */
# ifdef REGISTER_LIBRARIES_EARLY
START_WORLD();
GC_cond_register_dynamic_libraries();
STOP_WORLD();
# endif
GC_invalidate_mark_state();
GC_scan_ptr = NULL;
ret_val = FALSE;
goto rm_handler; /* Back to platform-specific code. */
}
#endif /* WRAP_MARK_SOME */
GC_INNER void GC_invalidate_mark_state(void)
{
GC_mark_state = MS_INVALID;
GC_mark_stack_top = GC_mark_stack-1;
}
GC_INNER mse * GC_signal_mark_stack_overflow(mse *msp)
{
GC_mark_state = MS_INVALID;
# ifdef PARALLEL_MARK
/* We are using a local_mark_stack in parallel mode, so */
/* do not signal the global mark stack to be resized. */
/* That will be done if required in GC_return_mark_stack. */
if (!GC_parallel)
GC_mark_stack_too_small = TRUE;
# else
GC_mark_stack_too_small = TRUE;
# endif
GC_COND_LOG_PRINTF("Mark stack overflow; current size = %lu entries\n",
(unsigned long)GC_mark_stack_size);
return(msp - GC_MARK_STACK_DISCARDS);
}
/*
* Mark objects pointed to by the regions described by
* mark stack entries between mark_stack and mark_stack_top,
* inclusive. Assumes the upper limit of a mark stack entry
* is never 0. A mark stack entry never has size 0.
* We try to traverse on the order of a hblk of memory before we return.
* Caller is responsible for calling this until the mark stack is empty.
* Note that this is the most performance critical routine in the
* collector. Hence it contains all sorts of ugly hacks to speed
* things up. In particular, we avoid procedure calls on the common
* path, we take advantage of peculiarities of the mark descriptor
* encoding, we optionally maintain a cache for the block address to
* header mapping, we prefetch when an object is "grayed", etc.
*/
GC_ATTR_NO_SANITIZE_ADDR GC_ATTR_NO_SANITIZE_MEMORY GC_ATTR_NO_SANITIZE_THREAD
GC_INNER mse * GC_mark_from(mse *mark_stack_top, mse *mark_stack,
mse *mark_stack_limit)
{
signed_word credit = HBLKSIZE; /* Remaining credit for marking work. */
ptr_t current_p; /* Pointer to current candidate ptr. */
word current; /* Candidate pointer. */
ptr_t limit = 0; /* (Incl) limit of current candidate range. */
word descr;
ptr_t greatest_ha = (ptr_t)GC_greatest_plausible_heap_addr;
ptr_t least_ha = (ptr_t)GC_least_plausible_heap_addr;
DECLARE_HDR_CACHE;
# define SPLIT_RANGE_WORDS 128 /* Must be power of 2. */
GC_objects_are_marked = TRUE;
INIT_HDR_CACHE;
# ifdef OS2 /* Use untweaked version to circumvent compiler problem. */
while ((word)mark_stack_top >= (word)mark_stack && credit >= 0)
# else
while (((((word)mark_stack_top - (word)mark_stack) | (word)credit)
& SIGNB) == 0)
# endif
{
current_p = mark_stack_top -> mse_start;
descr = mark_stack_top -> mse_descr.w;
retry:
/* current_p and descr describe the current object. */
/* (*mark_stack_top) is vacant. */
/* The following is 0 only for small objects described by a simple */
/* length descriptor. For many applications this is the common */
/* case, so we try to detect it quickly. */
if (descr & ((~(WORDS_TO_BYTES(SPLIT_RANGE_WORDS) - 1)) | GC_DS_TAGS)) {
word tag = descr & GC_DS_TAGS;
GC_STATIC_ASSERT(GC_DS_TAGS == 0x3);
switch(tag) {
case GC_DS_LENGTH:
/* Large length. */
/* Process part of the range to avoid pushing too much on the */
/* stack. */
GC_ASSERT(descr < (word)GC_greatest_plausible_heap_addr
- (word)GC_least_plausible_heap_addr
|| (word)(current_p + descr)
<= (word)GC_least_plausible_heap_addr
|| (word)current_p >= (word)GC_greatest_plausible_heap_addr);
# ifdef PARALLEL_MARK
# define SHARE_BYTES 2048
if (descr > SHARE_BYTES && GC_parallel
&& (word)mark_stack_top < (word)(mark_stack_limit - 1)) {
word new_size = (descr/2) & ~(word)(sizeof(word)-1);
mark_stack_top -> mse_start = current_p;
mark_stack_top -> mse_descr.w = new_size + sizeof(word);
/* Makes sure we handle */
/* misaligned pointers. */
mark_stack_top++;
# ifdef ENABLE_TRACE
if ((word)GC_trace_addr >= (word)current_p
&& (word)GC_trace_addr < (word)(current_p + descr)) {
GC_log_printf("GC #%u: large section; start %p, len %lu,"
" splitting (parallel) at %p\n",
(unsigned)GC_gc_no, (void *)current_p,
(unsigned long)descr,
(void *)(current_p + new_size));
}
# endif
current_p += new_size;
descr -= new_size;
goto retry;
}
# endif /* PARALLEL_MARK */
mark_stack_top -> mse_start =
limit = current_p + WORDS_TO_BYTES(SPLIT_RANGE_WORDS-1);
mark_stack_top -> mse_descr.w =
descr - WORDS_TO_BYTES(SPLIT_RANGE_WORDS-1);
# ifdef ENABLE_TRACE
if ((word)GC_trace_addr >= (word)current_p
&& (word)GC_trace_addr < (word)(current_p + descr)) {
GC_log_printf("GC #%u: large section; start %p, len %lu,"
" splitting at %p\n",
(unsigned)GC_gc_no, (void *)current_p,
(unsigned long)descr, (void *)limit);
}
# endif
/* Make sure that pointers overlapping the two ranges are */
/* considered. */
limit += sizeof(word) - ALIGNMENT;
break;
case GC_DS_BITMAP:
mark_stack_top--;
# ifdef ENABLE_TRACE
if ((word)GC_trace_addr >= (word)current_p
&& (word)GC_trace_addr < (word)(current_p
+ WORDS_TO_BYTES(WORDSZ-2))) {
GC_log_printf("GC #%u: tracing from %p bitmap descr %lu\n",
(unsigned)GC_gc_no, (void *)current_p,
(unsigned long)descr);
}
# endif /* ENABLE_TRACE */
descr &= ~GC_DS_TAGS;
credit -= WORDS_TO_BYTES(WORDSZ/2); /* guess */
while (descr != 0) {
if ((descr & SIGNB) != 0) {
current = *(word *)current_p;
FIXUP_POINTER(current);
if (current >= (word)least_ha && current < (word)greatest_ha) {
PREFETCH((ptr_t)current);
# ifdef ENABLE_TRACE
if (GC_trace_addr == current_p) {
GC_log_printf("GC #%u: considering(3) %p -> %p\n",
(unsigned)GC_gc_no, (void *)current_p,
(void *)current);
}
# endif /* ENABLE_TRACE */
PUSH_CONTENTS((ptr_t)current, mark_stack_top,
mark_stack_limit, current_p);
}
}
descr <<= 1;
current_p += sizeof(word);
}
continue;
case GC_DS_PROC:
mark_stack_top--;
# ifdef ENABLE_TRACE
if ((word)GC_trace_addr >= (word)current_p
&& GC_base(current_p) != 0
&& GC_base(current_p) == GC_base(GC_trace_addr)) {
GC_log_printf("GC #%u: tracing from %p, proc descr %lu\n",
(unsigned)GC_gc_no, (void *)current_p,
(unsigned long)descr);
}
# endif /* ENABLE_TRACE */
credit -= GC_PROC_BYTES;
mark_stack_top = (*PROC(descr))((word *)current_p, mark_stack_top,
mark_stack_limit, ENV(descr));
continue;
case GC_DS_PER_OBJECT:
if ((signed_word)descr >= 0) {
/* Descriptor is in the object. */
descr = *(word *)(current_p + descr - GC_DS_PER_OBJECT);
} else {
/* Descriptor is in type descriptor pointed to by first */
/* word in object. */
ptr_t type_descr = *(ptr_t *)current_p;
/* type_descr is either a valid pointer to the descriptor */
/* structure, or this object was on a free list. */
/* If it was anything but the last object on the free list, */
/* we will misinterpret the next object on the free list as */
/* the type descriptor, and get a 0 GC descriptor, which */
/* is ideal. Unfortunately, we need to check for the last */
/* object case explicitly. */
if (EXPECT(0 == type_descr, FALSE)) {
mark_stack_top--;
continue;
}
descr = *(word *)(type_descr
- ((signed_word)descr + (GC_INDIR_PER_OBJ_BIAS
- GC_DS_PER_OBJECT)));
}
if (0 == descr) {
/* Can happen either because we generated a 0 descriptor */
/* or we saw a pointer to a free object. */
mark_stack_top--;
continue;
}
goto retry;
}
} else {
/* Small object with length descriptor. */
mark_stack_top--;
# ifndef SMALL_CONFIG
if (descr < sizeof(word))
continue;
# endif
# ifdef ENABLE_TRACE
if ((word)GC_trace_addr >= (word)current_p
&& (word)GC_trace_addr < (word)(current_p + descr)) {
GC_log_printf("GC #%u: small object; start %p, len %lu\n",
(unsigned)GC_gc_no, (void *)current_p,
(unsigned long)descr);
}
# endif
limit = current_p + (word)descr;
}
/* The simple case in which we're scanning a range. */
GC_ASSERT(!((word)current_p & (ALIGNMENT-1)));
credit -= limit - current_p;
limit -= sizeof(word);
{
# define PREF_DIST 4
# ifndef SMALL_CONFIG
word deferred;
/* Try to prefetch the next pointer to be examined ASAP. */
/* Empirically, this also seems to help slightly without */
/* prefetches, at least on linux/X86. Presumably this loop */
/* ends up with less register pressure, and gcc thus ends up */
/* generating slightly better code. Overall gcc code quality */
/* for this loop is still not great. */
for(;;) {
PREFETCH(limit - PREF_DIST*CACHE_LINE_SIZE);
GC_ASSERT((word)limit >= (word)current_p);
deferred = *(word *)limit;
FIXUP_POINTER(deferred);
limit -= ALIGNMENT;
if (deferred >= (word)least_ha && deferred < (word)greatest_ha) {
PREFETCH((ptr_t)deferred);
break;
}
if ((word)current_p > (word)limit) goto next_object;
/* Unroll once, so we don't do too many of the prefetches */
/* based on limit. */
deferred = *(word *)limit;
FIXUP_POINTER(deferred);
limit -= ALIGNMENT;
if (deferred >= (word)least_ha && deferred < (word)greatest_ha) {
PREFETCH((ptr_t)deferred);
break;
}
if ((word)current_p > (word)limit) goto next_object;
}
# endif
while ((word)current_p <= (word)limit) {
/* Empirically, unrolling this loop doesn't help a lot. */
/* Since PUSH_CONTENTS expands to a lot of code, */
/* we don't. */
current = *(word *)current_p;
FIXUP_POINTER(current);
PREFETCH(current_p + PREF_DIST*CACHE_LINE_SIZE);
if (current >= (word)least_ha && current < (word)greatest_ha) {
/* Prefetch the contents of the object we just pushed. It's */
/* likely we will need them soon. */
PREFETCH((ptr_t)current);
# ifdef ENABLE_TRACE
if (GC_trace_addr == current_p) {
GC_log_printf("GC #%u: considering(1) %p -> %p\n",
(unsigned)GC_gc_no, (void *)current_p,
(void *)current);
}
# endif /* ENABLE_TRACE */
PUSH_CONTENTS((ptr_t)current, mark_stack_top,
mark_stack_limit, current_p);
}
current_p += ALIGNMENT;
}
# ifndef SMALL_CONFIG
/* We still need to mark the entry we previously prefetched. */
/* We already know that it passes the preliminary pointer */
/* validity test. */
# ifdef ENABLE_TRACE
if (GC_trace_addr == current_p) {
GC_log_printf("GC #%u: considering(2) %p -> %p\n",
(unsigned)GC_gc_no, (void *)current_p,
(void *)deferred);
}
# endif /* ENABLE_TRACE */
PUSH_CONTENTS((ptr_t)deferred, mark_stack_top,
mark_stack_limit, current_p);
next_object:;
# endif
}
}
return mark_stack_top;
}
#ifdef PARALLEL_MARK
STATIC GC_bool GC_help_wanted = FALSE; /* Protected by mark lock. */
STATIC unsigned GC_helper_count = 0; /* Number of running helpers. */
/* Protected by mark lock. */
STATIC unsigned GC_active_count = 0; /* Number of active helpers. */
/* Protected by mark lock. */
/* May increase and decrease */
/* within each mark cycle. But */
/* once it returns to 0, it */
/* stays zero for the cycle. */
GC_INNER word GC_mark_no = 0;
#ifdef LINT2
# define LOCAL_MARK_STACK_SIZE (HBLKSIZE / 8)
#else
# define LOCAL_MARK_STACK_SIZE HBLKSIZE
/* Under normal circumstances, this is big enough to guarantee */
/* we don't overflow half of it in a single call to */
/* GC_mark_from. */
#endif
/* Wait all markers to finish initialization (i.e. store */
/* marker_[b]sp, marker_mach_threads, GC_marker_Id). */
GC_INNER void GC_wait_for_markers_init(void)
{
signed_word count;
if (GC_markers_m1 == 0)
return;
/* Allocate the local mark stack for the thread that holds GC lock. */
# ifndef CAN_HANDLE_FORK
GC_ASSERT(NULL == GC_main_local_mark_stack);
# else
if (NULL == GC_main_local_mark_stack)
# endif
{
size_t bytes_to_get =
ROUNDUP_PAGESIZE_IF_MMAP(LOCAL_MARK_STACK_SIZE * sizeof(mse));
GC_main_local_mark_stack = (mse *)GET_MEM(bytes_to_get);
if (NULL == GC_main_local_mark_stack)
ABORT("Insufficient memory for main local_mark_stack");
GC_add_to_our_memory((ptr_t)GC_main_local_mark_stack, bytes_to_get);
}
/* Reuse marker lock and builders count to synchronize */
/* marker threads startup. */
GC_acquire_mark_lock();
GC_fl_builder_count += GC_markers_m1;
count = GC_fl_builder_count;
GC_release_mark_lock();
if (count != 0) {
GC_ASSERT(count > 0);
GC_wait_for_reclaim();
}
}
/* Steal mark stack entries starting at mse low into mark stack local */
/* until we either steal mse high, or we have max entries. */
/* Return a pointer to the top of the local mark stack. */
/* (*next) is replaced by a pointer to the next unscanned mark stack */
/* entry. */
STATIC mse * GC_steal_mark_stack(mse * low, mse * high, mse * local,
unsigned max, mse **next)
{
mse *p;
mse *top = local - 1;
unsigned i = 0;
GC_ASSERT((word)high >= (word)(low - 1)
&& (word)(high - low + 1) <= GC_mark_stack_size);
for (p = low; (word)p <= (word)high && i <= max; ++p) {
word descr = (word)AO_load(&p->mse_descr.ao);
if (descr != 0) {
/* Must be ordered after read of descr: */
AO_store_release_write(&p->mse_descr.ao, 0);
/* More than one thread may get this entry, but that's only */
/* a minor performance problem. */
++top;
top -> mse_descr.w = descr;
top -> mse_start = p -> mse_start;
GC_ASSERT((descr & GC_DS_TAGS) != GC_DS_LENGTH
|| descr < (word)GC_greatest_plausible_heap_addr
- (word)GC_least_plausible_heap_addr
|| (word)(p->mse_start + descr)
<= (word)GC_least_plausible_heap_addr
|| (word)p->mse_start
>= (word)GC_greatest_plausible_heap_addr);
/* If this is a big object, count it as */
/* size/256 + 1 objects. */
++i;
if ((descr & GC_DS_TAGS) == GC_DS_LENGTH) i += (int)(descr >> 8);
}
}
*next = p;
return top;
}
/* Copy back a local mark stack. */
/* low and high are inclusive bounds. */
STATIC void GC_return_mark_stack(mse * low, mse * high)
{
mse * my_top;
mse * my_start;
size_t stack_size;
if ((word)high < (word)low) return;
stack_size = high - low + 1;
GC_acquire_mark_lock();
my_top = GC_mark_stack_top; /* Concurrent modification impossible. */
my_start = my_top + 1;
if ((word)(my_start - GC_mark_stack + stack_size)
> (word)GC_mark_stack_size) {
GC_COND_LOG_PRINTF("No room to copy back mark stack\n");
GC_mark_state = MS_INVALID;
GC_mark_stack_too_small = TRUE;
/* We drop the local mark stack. We'll fix things later. */
} else {
BCOPY(low, my_start, stack_size * sizeof(mse));
GC_ASSERT((mse *)AO_load((volatile AO_t *)(&GC_mark_stack_top))
== my_top);