queue_internal.h   [plain text]

/*
 * Copyright (c) 2008-2011 Apple Inc. All rights reserved.
 *
 * @APPLE_APACHE_LICENSE_HEADER_START@
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * @APPLE_APACHE_LICENSE_HEADER_END@
 */

/*
 * IMPORTANT: This header file describes INTERNAL interfaces to libdispatch
 * which are subject to change in future releases of Mac OS X. Any applications
 * relying on these interfaces WILL break.
 */

#ifndef __DISPATCH_QUEUE_INTERNAL__
#define __DISPATCH_QUEUE_INTERNAL__

#ifndef __DISPATCH_INDIRECT__
#error "Please #include <dispatch/dispatch.h> instead of this file directly."
#include <dispatch/base.h> // for HeaderDoc
#endif

// If dc_vtable is less than 127, then the object is a continuation.
// Otherwise, the object has a private layout and memory management rules. The
// first two words must align with normal objects.
#define DISPATCH_CONTINUATION_HEADER(x) \
	const void *do_vtable; \
	struct x *volatile do_next; \
	dispatch_function_t dc_func; \
	void *dc_ctxt

#define DISPATCH_OBJ_ASYNC_BIT		0x1
#define DISPATCH_OBJ_BARRIER_BIT	0x2
#define DISPATCH_OBJ_GROUP_BIT		0x4
#define DISPATCH_OBJ_SYNC_SLOW_BIT	0x8
// vtables are pointers far away from the low page in memory
#define DISPATCH_OBJ_IS_VTABLE(x) ((unsigned long)(x)->do_vtable > 127ul)

struct dispatch_continuation_s {
	DISPATCH_CONTINUATION_HEADER(dispatch_continuation_s);
	dispatch_group_t dc_group;
	void *dc_data[3];
};

typedef struct dispatch_continuation_s *dispatch_continuation_t;

struct dispatch_queue_attr_vtable_s {
	DISPATCH_VTABLE_HEADER(dispatch_queue_attr_s);
};

struct dispatch_queue_attr_s {
	DISPATCH_STRUCT_HEADER(dispatch_queue_attr_s, dispatch_queue_attr_vtable_s);
};

struct dispatch_queue_vtable_s {
	DISPATCH_VTABLE_HEADER(dispatch_queue_s);
};

#define DISPATCH_QUEUE_MIN_LABEL_SIZE 64

#ifdef __LP64__
#define DISPATCH_QUEUE_CACHELINE_PAD 32
#else
#define DISPATCH_QUEUE_CACHELINE_PAD 8
#endif

#define DISPATCH_QUEUE_HEADER \
	uint32_t volatile dq_running; \
	uint32_t dq_width; \
	struct dispatch_object_s *volatile dq_items_tail; \
	struct dispatch_object_s *volatile dq_items_head; \
	unsigned long dq_serialnum; \
	dispatch_queue_t dq_specific_q;

struct dispatch_queue_s {
	DISPATCH_STRUCT_HEADER(dispatch_queue_s, dispatch_queue_vtable_s);
	DISPATCH_QUEUE_HEADER;
	char dq_label[DISPATCH_QUEUE_MIN_LABEL_SIZE]; // must be last
	char _dq_pad[DISPATCH_QUEUE_CACHELINE_PAD]; // for static queues only
};

extern struct dispatch_queue_s _dispatch_mgr_q;

void _dispatch_queue_dispose(dispatch_queue_t dq);
void _dispatch_queue_invoke(dispatch_queue_t dq);
void _dispatch_queue_push_list_slow(dispatch_queue_t dq,
		struct dispatch_object_s *obj);

DISPATCH_ALWAYS_INLINE
static inline void
_dispatch_queue_push_list(dispatch_queue_t dq, dispatch_object_t _head,
		dispatch_object_t _tail)
{
	struct dispatch_object_s *prev, *head = _head._do, *tail = _tail._do;

	tail->do_next = NULL;
	dispatch_atomic_store_barrier();
	prev = fastpath(dispatch_atomic_xchg2o(dq, dq_items_tail, tail));
	if (prev) {
		// if we crash here with a value less than 0x1000, then we are at a
		// known bug in client code for example, see _dispatch_queue_dispose
		// or _dispatch_atfork_child
		prev->do_next = head;
	} else {
		_dispatch_queue_push_list_slow(dq, head);
	}
}

#define _dispatch_queue_push(x, y) _dispatch_queue_push_list((x), (y), (y))

#if DISPATCH_DEBUG
void dispatch_debug_queue(dispatch_queue_t dq, const char* str);
#else
static inline void dispatch_debug_queue(dispatch_queue_t dq DISPATCH_UNUSED,
		const char* str DISPATCH_UNUSED) {}
#endif

size_t dispatch_queue_debug(dispatch_queue_t dq, char* buf, size_t bufsiz);
size_t _dispatch_queue_debug_attr(dispatch_queue_t dq, char* buf,
		size_t bufsiz);

DISPATCH_ALWAYS_INLINE
static inline dispatch_queue_t
_dispatch_queue_get_current(void)
{
	return _dispatch_thread_getspecific(dispatch_queue_key);
}

#define DISPATCH_QUEUE_PRIORITY_COUNT 4
#define DISPATCH_ROOT_QUEUE_COUNT (DISPATCH_QUEUE_PRIORITY_COUNT * 2)

// overcommit priority index values need bit 1 set
enum {
	DISPATCH_ROOT_QUEUE_IDX_LOW_PRIORITY = 0,
	DISPATCH_ROOT_QUEUE_IDX_LOW_OVERCOMMIT_PRIORITY,
	DISPATCH_ROOT_QUEUE_IDX_DEFAULT_PRIORITY,
	DISPATCH_ROOT_QUEUE_IDX_DEFAULT_OVERCOMMIT_PRIORITY,
	DISPATCH_ROOT_QUEUE_IDX_HIGH_PRIORITY,
	DISPATCH_ROOT_QUEUE_IDX_HIGH_OVERCOMMIT_PRIORITY,
	DISPATCH_ROOT_QUEUE_IDX_BACKGROUND_PRIORITY,
	DISPATCH_ROOT_QUEUE_IDX_BACKGROUND_OVERCOMMIT_PRIORITY,
};

extern const struct dispatch_queue_attr_vtable_s dispatch_queue_attr_vtable;
extern const struct dispatch_queue_vtable_s _dispatch_queue_vtable;
extern unsigned long _dispatch_queue_serial_numbers;
extern struct dispatch_queue_s _dispatch_root_queues[];

DISPATCH_ALWAYS_INLINE DISPATCH_CONST
static inline dispatch_queue_t
_dispatch_get_root_queue(long priority, bool overcommit)
{
	if (overcommit) switch (priority) {
	case DISPATCH_QUEUE_PRIORITY_LOW:
		return &_dispatch_root_queues[
				DISPATCH_ROOT_QUEUE_IDX_LOW_OVERCOMMIT_PRIORITY];
	case DISPATCH_QUEUE_PRIORITY_DEFAULT:
		return &_dispatch_root_queues[
				DISPATCH_ROOT_QUEUE_IDX_DEFAULT_OVERCOMMIT_PRIORITY];
	case DISPATCH_QUEUE_PRIORITY_HIGH:
		return &_dispatch_root_queues[
				DISPATCH_ROOT_QUEUE_IDX_HIGH_OVERCOMMIT_PRIORITY];
	case DISPATCH_QUEUE_PRIORITY_BACKGROUND:
		return &_dispatch_root_queues[
				DISPATCH_ROOT_QUEUE_IDX_BACKGROUND_OVERCOMMIT_PRIORITY];
	}
	switch (priority) {
	case DISPATCH_QUEUE_PRIORITY_LOW:
		return &_dispatch_root_queues[DISPATCH_ROOT_QUEUE_IDX_LOW_PRIORITY];
	case DISPATCH_QUEUE_PRIORITY_DEFAULT:
		return &_dispatch_root_queues[DISPATCH_ROOT_QUEUE_IDX_DEFAULT_PRIORITY];
	case DISPATCH_QUEUE_PRIORITY_HIGH:
		return &_dispatch_root_queues[DISPATCH_ROOT_QUEUE_IDX_HIGH_PRIORITY];
	case DISPATCH_QUEUE_PRIORITY_BACKGROUND:
		return &_dispatch_root_queues[
				DISPATCH_ROOT_QUEUE_IDX_BACKGROUND_PRIORITY];
	default:
		return NULL;
	}
}

// Note to later developers: ensure that any initialization changes are
// made for statically allocated queues (i.e. _dispatch_main_q).
static inline void
_dispatch_queue_init(dispatch_queue_t dq)
{
	dq->do_vtable = &_dispatch_queue_vtable;
	dq->do_next = DISPATCH_OBJECT_LISTLESS;
	dq->do_ref_cnt = 1;
	dq->do_xref_cnt = 1;
	// Default target queue is overcommit!
	dq->do_targetq = _dispatch_get_root_queue(0, true);
	dq->dq_running = 0;
	dq->dq_width = 1;
	dq->dq_serialnum = dispatch_atomic_inc(&_dispatch_queue_serial_numbers) - 1;
}

#endif