xref: /dports/lang/mono/mono-5.10.1.57/mono/sgen/sgen-pinning.c

/**
 * \file
 * The pin queue.
 *
 * Copyright 2001-2003 Ximian, Inc
 * Copyright 2003-2010 Novell, Inc.
 * Copyright (C) 2012 Xamarin Inc
 *
 * Licensed under the MIT license. See LICENSE file in the project root for full license information.
 */

#include "config.h"
#ifdef HAVE_SGEN_GC

#include <string.h>

#include "mono/sgen/sgen-gc.h"
#include "mono/sgen/sgen-pinning.h"
#include "mono/sgen/sgen-protocol.h"
#include "mono/sgen/sgen-pointer-queue.h"
#include "mono/sgen/sgen-client.h"

static SgenPointerQueue pin_queue;
static size_t last_num_pinned = 0;
/*
 * While we hold the pin_queue_mutex, all objects in pin_queue_objs will
 * stay pinned, which means they can't move, therefore they can be scanned.
 */
static SgenPointerQueue pin_queue_objs;
static mono_mutex_t pin_queue_mutex;

#define PIN_HASH_SIZE 1024
static void *pin_hash_filter [PIN_HASH_SIZE];

void
sgen_pinning_init (void)
{
	mono_os_mutex_init (&pin_queue_mutex);
}

void
sgen_init_pinning (void)
{
	memset (pin_hash_filter, 0, sizeof (pin_hash_filter));
	pin_queue.mem_type = INTERNAL_MEM_PIN_QUEUE;
}

void
sgen_init_pinning_for_conc (void)
{
	mono_os_mutex_lock (&pin_queue_mutex);
	sgen_pointer_queue_clear (&pin_queue_objs);
}

void
sgen_finish_pinning (void)
{
	last_num_pinned = pin_queue.next_slot;
	sgen_pointer_queue_clear (&pin_queue);
}

void
sgen_finish_pinning_for_conc (void)
{
	mono_os_mutex_unlock (&pin_queue_mutex);
}

void
sgen_pinning_register_pinned_in_nursery (GCObject *obj)
{
	sgen_pointer_queue_add (&pin_queue_objs, obj);
}

void
sgen_scan_pin_queue_objects (ScanCopyContext ctx)
{
	int i;
	ScanObjectFunc scan_func = ctx.ops->scan_object;

	mono_os_mutex_lock (&pin_queue_mutex);
	for (i = 0; i < pin_queue_objs.next_slot; ++i) {
		GCObject *obj = (GCObject *)pin_queue_objs.data [i];
		scan_func (obj, sgen_obj_get_descriptor_safe (obj), ctx.queue);
	}
	mono_os_mutex_unlock (&pin_queue_mutex);
}

void
sgen_pin_stage_ptr (void *ptr)
{
	/*very simple multiplicative hash function, tons better than simple and'ng */
	int hash_idx = ((mword)ptr * 1737350767) & (PIN_HASH_SIZE - 1);
	if (pin_hash_filter [hash_idx] == ptr)
		return;

	pin_hash_filter [hash_idx] = ptr;

	sgen_pointer_queue_add (&pin_queue, ptr);
}

gboolean
sgen_find_optimized_pin_queue_area (void *start, void *end, size_t *first_out, size_t *last_out)
{
	size_t first = sgen_pointer_queue_search (&pin_queue, start);
	size_t last = sgen_pointer_queue_search (&pin_queue, end);
	SGEN_ASSERT (0, last == pin_queue.next_slot || pin_queue.data [last] >= end, "Pin queue search gone awry");
	*first_out = first;
	*last_out = last;
	return first != last;
}

void**
sgen_pinning_get_entry (size_t index)
{
	SGEN_ASSERT (0, index <= pin_queue.next_slot, "Pin queue entry out of range");
	return &pin_queue.data [index];
}

void
sgen_find_section_pin_queue_start_end (GCMemSection *section)
{
	SGEN_LOG (6, "Pinning from section %p (%p-%p)", section, section->data, section->end_data);

	sgen_find_optimized_pin_queue_area (section->data, section->end_data,
			&section->pin_queue_first_entry, &section->pin_queue_last_entry);

	SGEN_LOG (6, "Found %zd pinning addresses in section %p",
			section->pin_queue_last_entry - section->pin_queue_first_entry, section);
}

/*This will setup the given section for the while pin queue. */
void
sgen_pinning_setup_section (GCMemSection *section)
{
	section->pin_queue_first_entry = 0;
	section->pin_queue_last_entry = pin_queue.next_slot;
}

void
sgen_pinning_trim_queue_to_section (GCMemSection *section)
{
	SGEN_ASSERT (0, section->pin_queue_first_entry == 0, "Pin queue trimming assumes the whole pin queue is used by the nursery");
	pin_queue.next_slot = section->pin_queue_last_entry;
}

/*
 * This is called when we've run out of memory during a major collection.
 *
 * After collecting potential pin entries and sorting the array, this is what it looks like:
 *
 * +--------------------+---------------------------------------------+--------------------+
 * | major heap entries |               nursery entries               | major heap entries |
 * +--------------------+---------------------------------------------+--------------------+
 *
 * Of course there might not be major heap entries before and/or after the nursery entries,
 * depending on where the major heap sections are in the address space, and whether there
 * were any potential pointers there.
 *
 * When we pin nursery objects, we compact the nursery part of the pin array, which leaves
 * discarded entries after the ones that actually pointed to nursery objects:
 *
 * +--------------------+-----------------+---------------------------+--------------------+
 * | major heap entries | nursery entries | discarded nursery entries | major heap entries |
 * +--------------------+-----------------+---------------------------+--------------------+
 *
 * When, due to being out of memory, we late pin more objects, the pin array looks like
 * this:
 *
 * +--------------------+-----------------+---------------------------+--------------------+--------------+
 * | major heap entries | nursery entries | discarded nursery entries | major heap entries | late entries |
 * +--------------------+-----------------+---------------------------+--------------------+--------------+
 *
 * This function gets rid of the discarded nursery entries by nulling them out.  Note that
 * we can late pin objects not only in the nursery but also in the major heap, which happens
 * when evacuation fails.
 */
void
sgen_pin_queue_clear_discarded_entries (GCMemSection *section, size_t max_pin_slot)
{
	void **start = sgen_pinning_get_entry (section->pin_queue_last_entry);
	void **end = sgen_pinning_get_entry (max_pin_slot);
	void *addr;

	for (; start < end; ++start) {
		addr = *start;
		if ((char*)addr < section->data || (char*)addr > section->end_data)
			break;
		*start = NULL;
	}
}

/* reduce the info in the pin queue, removing duplicate pointers and sorting them */
void
sgen_optimize_pin_queue (void)
{
	sgen_pointer_queue_sort_uniq (&pin_queue);
}

size_t
sgen_get_pinned_count (void)
{
	return pin_queue.next_slot;
}

void
sgen_dump_pin_queue (void)
{
	int i;

	for (i = 0; i < last_num_pinned; ++i) {
		GCObject *ptr = (GCObject *)pin_queue.data [i];
		SGEN_LOG (3, "Bastard pinning obj %p (%s), size: %zd", ptr, sgen_client_vtable_get_name (SGEN_LOAD_VTABLE (ptr)), sgen_safe_object_get_size (ptr));
	}
}

typedef struct _CementHashEntry CementHashEntry;
struct _CementHashEntry {
	GCObject *obj;
	unsigned int count;
	gboolean forced; /* if it should stay cemented after the finishing pause */
};

static CementHashEntry cement_hash [SGEN_CEMENT_HASH_SIZE];

static gboolean cement_enabled = TRUE;

void
sgen_cement_init (gboolean enabled)
{
	cement_enabled = enabled;
}

void
sgen_cement_reset (void)
{
	int i;
	for (i = 0; i < SGEN_CEMENT_HASH_SIZE; i++) {
		if (cement_hash [i].forced) {
			cement_hash [i].forced = FALSE;
		} else {
			cement_hash [i].obj = NULL;
			cement_hash [i].count = 0;
		}
	}
	binary_protocol_cement_reset ();
}


/*
 * The pin_queue should be full and sorted, without entries from the cemented
 * objects. We traverse the cement hash and check if each object is pinned in
 * the pin_queue (the pin_queue contains entries between obj and obj+obj_len)
 */
void
sgen_cement_force_pinned (void)
{
	int i;

	if (!cement_enabled)
		return;

	for (i = 0; i < SGEN_CEMENT_HASH_SIZE; i++) {
		GCObject *obj = cement_hash [i].obj;
		size_t index;
		if (!obj)
			continue;
		if (cement_hash [i].count < SGEN_CEMENT_THRESHOLD)
			continue;
		SGEN_ASSERT (0, !cement_hash [i].forced, "Why do we have a forced cemented object before forcing ?");

		/* Returns the index of the target or of the first element greater than it */
		index = sgen_pointer_queue_search (&pin_queue, obj);
		if (index == pin_queue.next_slot)
			continue;
		SGEN_ASSERT (0, pin_queue.data [index] >= (gpointer)obj, "Binary search should return a pointer greater than the search target");
		if (pin_queue.data [index] < (gpointer)((char*)obj + sgen_safe_object_get_size (obj)))
			cement_hash [i].forced = TRUE;
	}
}

gboolean
sgen_cement_is_forced (GCObject *obj)
{
	guint hv = sgen_aligned_addr_hash (obj);
	int i = SGEN_CEMENT_HASH (hv);

	SGEN_ASSERT (5, sgen_ptr_in_nursery (obj), "Looking up cementing for non-nursery objects makes no sense");

	if (!cement_enabled)
		return FALSE;

	if (!cement_hash [i].obj)
		return FALSE;
	if (cement_hash [i].obj != obj)
		return FALSE;

	return cement_hash [i].forced;
}

gboolean
sgen_cement_lookup (GCObject *obj)
{
	guint hv = sgen_aligned_addr_hash (obj);
	int i = SGEN_CEMENT_HASH (hv);

	SGEN_ASSERT (5, sgen_ptr_in_nursery (obj), "Looking up cementing for non-nursery objects makes no sense");

	if (!cement_enabled)
		return FALSE;

	if (!cement_hash [i].obj)
		return FALSE;
	if (cement_hash [i].obj != obj)
		return FALSE;

	return cement_hash [i].count >= SGEN_CEMENT_THRESHOLD;
}

gboolean
sgen_cement_lookup_or_register (GCObject *obj)
{
	guint hv;
	int i;
	CementHashEntry *hash = cement_hash;

	if (!cement_enabled)
		return FALSE;

	hv = sgen_aligned_addr_hash (obj);
	i = SGEN_CEMENT_HASH (hv);

	SGEN_ASSERT (5, sgen_ptr_in_nursery (obj), "Can only cement pointers to nursery objects");

	if (!hash [i].obj) {
		GCObject *old_obj;
		old_obj = mono_atomic_cas_ptr ((gpointer*)&hash [i].obj, obj, NULL);
		/* Check if the slot was occupied by some other object */
		if (old_obj != NULL && old_obj != obj)
			return FALSE;
	} else if (hash [i].obj != obj) {
		return FALSE;
	}

	if (hash [i].count >= SGEN_CEMENT_THRESHOLD)
		return TRUE;

	if (mono_atomic_inc_i32 ((gint32*)&hash [i].count) == SGEN_CEMENT_THRESHOLD) {
		SGEN_ASSERT (9, sgen_get_current_collection_generation () >= 0, "We can only cement objects when we're in a collection pause.");
		SGEN_ASSERT (9, SGEN_OBJECT_IS_PINNED (obj), "Can only cement pinned objects");
		SGEN_CEMENT_OBJECT (obj);

		binary_protocol_cement (obj, (gpointer)SGEN_LOAD_VTABLE (obj),
				(int)sgen_safe_object_get_size (obj));
	}

	return FALSE;
}

static void
pin_from_hash (CementHashEntry *hash, gboolean has_been_reset)
{
	int i;
	for (i = 0; i < SGEN_CEMENT_HASH_SIZE; ++i) {
		if (!hash [i].count)
			continue;

		if (has_been_reset)
			SGEN_ASSERT (5, hash [i].count >= SGEN_CEMENT_THRESHOLD, "Cementing hash inconsistent");

		sgen_pin_stage_ptr (hash [i].obj);
		binary_protocol_cement_stage (hash [i].obj);
		/* FIXME: do pin stats if enabled */

		SGEN_CEMENT_OBJECT (hash [i].obj);
	}
}

void
sgen_pin_cemented_objects (void)
{
	pin_from_hash (cement_hash, TRUE);
}

void
sgen_cement_clear_below_threshold (void)
{
	int i;
	for (i = 0; i < SGEN_CEMENT_HASH_SIZE; ++i) {
		if (cement_hash [i].count < SGEN_CEMENT_THRESHOLD) {
			cement_hash [i].obj = NULL;
			cement_hash [i].count = 0;
		}
	}
}

#endif /* HAVE_SGEN_GC */