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Fix task scanning for the Julia GC #2969

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Nov 12, 2018
Merged

Fix task scanning for the Julia GC #2969

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64 changes: 53 additions & 11 deletions src/julia_gc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -362,7 +362,6 @@ static jl_module_t * Module;
static jl_datatype_t * datatype_mptr;
static jl_datatype_t * datatype_bag;
static jl_datatype_t * datatype_largebag;
static Bag * StackBottomBags;
static UInt StackAlignBags;
static jl_ptls_t JuliaTLS, SaveTLS;
static size_t max_pool_obj_size;
Expand Down Expand Up @@ -474,15 +473,32 @@ static void TryMark(void * p)
}
}

static void TryMarkRangeReverse(void * start, void * end)
{
if (lt_ptr(end, start)) {
SWAP(void *, start, end);
}
char * p = (char *)(align_ptr(start));
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char * q = (char *)end - sizeof(void *);
while (!lt_ptr(q, p)) {
void * addr = *(void **)q;
if (addr)
TryMark(addr);
q -= StackAlignBags;
}
}

static void TryMarkRange(void * start, void * end)
{
if (lt_ptr(end, start)) {
SWAP(void *, start, end);
}
char * p = align_ptr(start);
char * p = (char *)align_ptr(start);
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char * q = (char *)end - sizeof(void *) + StackAlignBags;
while (lt_ptr(p, q)) {
TryMark(*(void **)p);
void * addr = *(void **)p;
if (addr)
TryMark(addr);
p += StackAlignBags;
}
}
Expand All @@ -502,6 +518,14 @@ void GapRootScanner(int full)
// mark our Julia module (this contains references to our custom data
// types, which thus also will not be collected prematurely)
JMark(Module);
jl_task_t * task = JuliaTLS->current_task;
size_t size;
int tid;
// We figure out the end of the stack from the current task. While
// `stack_bottom` is passed to InitBags(), we cannot use that if
// current_task != root_task.
char * stackend = (char *)jl_task_stack_buffer(task, &size, &tid);
stackend += size;

// allow installing a custom marking function. This is used for
// integrating GAP (possibly linked as a shared library) with other code
Expand All @@ -514,7 +538,7 @@ void GapRootScanner(int full)
syJmp_buf registers;
sySetjmp(registers);
TryMarkRange(registers, (char *)registers + sizeof(syJmp_buf));
TryMarkRange((char *)registers + sizeof(syJmp_buf), StackBottomBags);
TryMarkRange((char *)registers + sizeof(syJmp_buf), stackend);

// mark all global objects
for (Int i = 0; i < GlobalCount; i++) {
Expand All @@ -529,9 +553,29 @@ void GapTaskScanner(jl_task_t * task, int root_task)
{
size_t size;
int tid;
void * stack = jl_task_stack_buffer(task, &size, &tid);
char * stack = (char *)jl_task_stack_buffer(task, &size, &tid);
if (stack && tid < 0) {
TryMarkRange(stack, (char *)stack + size);
if (task->copy_stack) {
// We know which part of the task stack is actually used,
// so we shorten the range we have to scan.
stack = stack + size - task->copy_stack;
size = task->copy_stack;
}
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volatile jl_jmp_buf * old_safe_restore =
(volatile jl_jmp_buf *)JuliaTLS->safe_restore;
jl_jmp_buf exc_buf;
if (!jl_setjmp(exc_buf, 0)) {
// The bottom of the stack may be protected with
// guard pages; accessing these results in segmentation
// faults. Julia catches those segmentation faults and
// longjmps to JuliaTLS->safe_restore; we use this
// mechamism to abort stack scanning when a protected
// page is hit. For this to work, we must scan the stack
// from top to bottom, so we see any guard pages last.
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JuliaTLS->safe_restore = &exc_buf;
TryMarkRangeReverse(stack, stack + size);
}
JuliaTLS->safe_restore = (jl_jmp_buf *)old_safe_restore;
}
}

Expand Down Expand Up @@ -633,7 +677,6 @@ void InitBags(UInt initial_size, Bag * stack_bottom, UInt stack_align)
GAP_ASSERT(jl_is_datatype(datatype_mptr));
GAP_ASSERT(jl_is_datatype(datatype_bag));
GAP_ASSERT(jl_is_datatype(datatype_largebag));
StackBottomBags = stack_bottom;
StackAlignBags = stack_align;
}

Expand All @@ -647,7 +690,7 @@ UInt CollectBags(UInt size, UInt full)
void RetypeBag(Bag bag, UInt new_type)
{
BagHeader * header = BAG_HEADER(bag);
UInt old_type = header->type;
UInt old_type = header->type;

#ifdef COUNT_BAGS
/* update the statistics */
Expand Down Expand Up @@ -685,8 +728,6 @@ void RetypeBag(Bag bag, UInt new_type)
// of supporting a feature nobody uses right now, we error out and
// wait to see if somebody complains.
Panic("cannot change bag type to one which requires a 'free' callback");


}
header->type = new_type;
}
Expand Down Expand Up @@ -805,7 +846,8 @@ inline void MarkBag(Bag bag)
MarkCacheCollisions++;
#endif
MarkCache[hash] = bag;
} else {
}
else {
#ifdef STAT_MARK_CACHE
MarkCacheHits++;
#endif
Expand Down