1、源码版本
libdispatch-1173.40.5
地址：https://opensource.apple.com/tarballs/libdispatch/
2、dispatch_get_global_queue
init.c
dispatch_queue_global_t
dispatch_get_global_queue(long priority, unsigned long flags)
{
dispatch_assert(countof(_dispatch_root_queues) ==
DISPATCH_ROOT_QUEUE_COUNT);
if (flags & ~(unsigned long)DISPATCH_QUEUE_OVERCOMMIT) {
return DISPATCH_BAD_INPUT;
}
// 获取队列优先级
dispatch_qos_t qos = _dispatch_qos_from_queue_priority(priority);
#if !HAVE_PTHREAD_WORKQUEUE_QOS
if (qos == QOS_CLASS_MAINTENANCE) {
qos = DISPATCH_QOS_BACKGROUND;
} else if (qos == QOS_CLASS_USER_INTERACTIVE) {
qos = DISPATCH_QOS_USER_INITIATED;
}
#endif
if (qos == DISPATCH_QOS_UNSPECIFIED) {
return DISPATCH_BAD_INPUT;
}
// 从系统默认的root队列数组中取对应qos的队列
return _dispatch_get_root_queue(qos, flags & DISPATCH_QUEUE_OVERCOMMIT);
}
priority.h
static inline dispatch_qos_t
_dispatch_qos_from_queue_priority(long priority)
{
switch (priority) {
case DISPATCH_QUEUE_PRIORITY_BACKGROUND: return DISPATCH_QOS_BACKGROUND;
case DISPATCH_QUEUE_PRIORITY_NON_INTERACTIVE: return DISPATCH_QOS_UTILITY;
case DISPATCH_QUEUE_PRIORITY_LOW: return DISPATCH_QOS_UTILITY;
case DISPATCH_QUEUE_PRIORITY_DEFAULT: return DISPATCH_QOS_DEFAULT;
case DISPATCH_QUEUE_PRIORITY_HIGH: return DISPATCH_QOS_USER_INITIATED;
default: return _dispatch_qos_from_qos_class((qos_class_t)priority);
}
}
inline_internal.h
struct dispatch_queue_global_s _dispatch_root_queues[] = {
#define _DISPATCH_ROOT_QUEUE_IDX(n, flags) \
((flags & DISPATCH_PRIORITY_FLAG_OVERCOMMIT) ? \
DISPATCH_ROOT_QUEUE_IDX_##n##_QOS_OVERCOMMIT : \
DISPATCH_ROOT_QUEUE_IDX_##n##_QOS)
#define _DISPATCH_ROOT_QUEUE_ENTRY(n, flags, ...) \
[_DISPATCH_ROOT_QUEUE_IDX(n, flags)] = { \
DISPATCH_GLOBAL_OBJECT_HEADER(queue_global), \
.dq_state = DISPATCH_ROOT_QUEUE_STATE_INIT_VALUE, \
.do_ctxt = _dispatch_root_queue_ctxt(_DISPATCH_ROOT_QUEUE_IDX(n, flags)), \
.dq_atomic_flags = DQF_WIDTH(DISPATCH_QUEUE_WIDTH_POOL), \
.dq_priority = flags | ((flags & DISPATCH_PRIORITY_FLAG_FALLBACK) ? \
_dispatch_priority_make_fallback(DISPATCH_QOS_##n) : \
_dispatch_priority_make(DISPATCH_QOS_##n, 0)), \
__VA_ARGS__ \
}
_DISPATCH_ROOT_QUEUE_ENTRY(MAINTENANCE, 0,
.dq_label = "com.apple.root.maintenance-qos",
.dq_serialnum = 4,
),
_DISPATCH_ROOT_QUEUE_ENTRY(MAINTENANCE, DISPATCH_PRIORITY_FLAG_OVERCOMMIT,
.dq_label = "com.apple.root.maintenance-qos.overcommit",
.dq_serialnum = 5,
),
_DISPATCH_ROOT_QUEUE_ENTRY(BACKGROUND, 0,
.dq_label = "com.apple.root.background-qos",
.dq_serialnum = 6,
),
_DISPATCH_ROOT_QUEUE_ENTRY(BACKGROUND, DISPATCH_PRIORITY_FLAG_OVERCOMMIT,
.dq_label = "com.apple.root.background-qos.overcommit",
.dq_serialnum = 7,
),
_DISPATCH_ROOT_QUEUE_ENTRY(UTILITY, 0,
.dq_label = "com.apple.root.utility-qos",
.dq_serialnum = 8,
),
_DISPATCH_ROOT_QUEUE_ENTRY(UTILITY, DISPATCH_PRIORITY_FLAG_OVERCOMMIT,
.dq_label = "com.apple.root.utility-qos.overcommit",
.dq_serialnum = 9,
),
_DISPATCH_ROOT_QUEUE_ENTRY(DEFAULT, DISPATCH_PRIORITY_FLAG_FALLBACK,
.dq_label = "com.apple.root.default-qos",
.dq_serialnum = 10,
),
_DISPATCH_ROOT_QUEUE_ENTRY(DEFAULT,
DISPATCH_PRIORITY_FLAG_FALLBACK | DISPATCH_PRIORITY_FLAG_OVERCOMMIT,
.dq_label = "com.apple.root.default-qos.overcommit",
.dq_serialnum = 11,
),
_DISPATCH_ROOT_QUEUE_ENTRY(USER_INITIATED, 0,
.dq_label = "com.apple.root.user-initiated-qos",
.dq_serialnum = 12,
),
_DISPATCH_ROOT_QUEUE_ENTRY(USER_INITIATED, DISPATCH_PRIORITY_FLAG_OVERCOMMIT,
.dq_label = "com.apple.root.user-initiated-qos.overcommit",
.dq_serialnum = 13,
),
_DISPATCH_ROOT_QUEUE_ENTRY(USER_INTERACTIVE, 0,
.dq_label = "com.apple.root.user-interactive-qos",
.dq_serialnum = 14,
),
_DISPATCH_ROOT_QUEUE_ENTRY(USER_INTERACTIVE, DISPATCH_PRIORITY_FLAG_OVERCOMMIT,
.dq_label = "com.apple.root.user-interactive-qos.overcommit",
.dq_serialnum = 15,
),
};
3、dispatch_queue_create
queue.c
dispatch_queue_t
dispatch_queue_create_with_target(const char *label, dispatch_queue_attr_t dqa,
dispatch_queue_t tq)
{
return _dispatch_lane_create_with_target(label, dqa, tq, false);
}
DISPATCH_NOINLINE
static dispatch_queue_t
_dispatch_lane_create_with_target(const char *label, dispatch_queue_attr_t dqa,
dispatch_queue_t tq, bool legacy)
{
dispatch_queue_attr_info_t dqai = _dispatch_queue_attr_to_info(dqa);
//
// Step 1: Normalize arguments (qos, overcommit, tq)
//
// 取出优先级
dispatch_qos_t qos = dqai.dqai_qos;
#if !HAVE_PTHREAD_WORKQUEUE_QOS
if (qos == DISPATCH_QOS_USER_INTERACTIVE) {
dqai.dqai_qos = qos = DISPATCH_QOS_USER_INITIATED;
}
if (qos == DISPATCH_QOS_MAINTENANCE) {
dqai.dqai_qos = qos = DISPATCH_QOS_BACKGROUND;
}
#endif // !HAVE_PTHREAD_WORKQUEUE_QOS
_dispatch_queue_attr_overcommit_t overcommit = dqai.dqai_overcommit;
if (overcommit != _dispatch_queue_attr_overcommit_unspecified && tq) {
if (tq->do_targetq) {
DISPATCH_CLIENT_CRASH(tq, "Cannot specify both overcommit and "
"a non-global target queue");
}
}
if (tq && dx_type(tq) == DISPATCH_QUEUE_GLOBAL_ROOT_TYPE) {
// Handle discrepancies between attr and target queue, attributes win
if (overcommit == _dispatch_queue_attr_overcommit_unspecified) {
if (tq->dq_priority & DISPATCH_PRIORITY_FLAG_OVERCOMMIT) {
overcommit = _dispatch_queue_attr_overcommit_enabled;
} else {
overcommit = _dispatch_queue_attr_overcommit_disabled;
}
}
if (qos == DISPATCH_QOS_UNSPECIFIED) {
qos = _dispatch_priority_qos(tq->dq_priority);
}
tq = NULL;
} else if (tq && !tq->do_targetq) {
// target is a pthread or runloop root queue, setting QoS or overcommit
// is disallowed
if (overcommit != _dispatch_queue_attr_overcommit_unspecified) {
DISPATCH_CLIENT_CRASH(tq, "Cannot specify an overcommit attribute "
"and use this kind of target queue");
}
} else {
if (overcommit == _dispatch_queue_attr_overcommit_unspecified) {
// Serial queues default to overcommit!
overcommit = dqai.dqai_concurrent ?
_dispatch_queue_attr_overcommit_disabled :
_dispatch_queue_attr_overcommit_enabled;
}
}
// 初始化队列默认传了DISPATCH_TARGET_QUEUE_DEFAULT，也就是null，所以进入if语句。
if (!tq) {
// 获取一个管理自己队列的root队列
tq = _dispatch_get_root_queue(
qos == DISPATCH_QOS_UNSPECIFIED ? DISPATCH_QOS_DEFAULT : qos,
overcommit == _dispatch_queue_attr_overcommit_enabled)->_as_dq;
if (unlikely(!tq)) {
DISPATCH_CLIENT_CRASH(qos, "Invalid queue attribute");
}
}
//
// Step 2: Initialize the queue
//
if (legacy) {
// if any of these attributes is specified, use non legacy classes
if (dqai.dqai_inactive || dqai.dqai_autorelease_frequency) {
legacy = false;
}
}
const void *vtable;
dispatch_queue_flags_t dqf = legacy ? DQF_MUTABLE : 0;
if (dqai.dqai_concurrent) {
vtable = DISPATCH_VTABLE(queue_concurrent);
} else {
vtable = DISPATCH_VTABLE(queue_serial);
}
switch (dqai.dqai_autorelease_frequency) {
case DISPATCH_AUTORELEASE_FREQUENCY_NEVER:
dqf |= DQF_AUTORELEASE_NEVER;
break;
case DISPATCH_AUTORELEASE_FREQUENCY_WORK_ITEM:
dqf |= DQF_AUTORELEASE_ALWAYS;
break;
}
if (label) {
const char *tmp = _dispatch_strdup_if_mutable(label);
if (tmp != label) {
dqf |= DQF_LABEL_NEEDS_FREE;
label = tmp;
}
}
dispatch_lane_t dq = _dispatch_object_alloc(vtable,
sizeof(struct dispatch_lane_s));
_dispatch_queue_init(dq, dqf, dqai.dqai_concurrent ?
DISPATCH_QUEUE_WIDTH_MAX : 1, DISPATCH_QUEUE_ROLE_INNER |
(dqai.dqai_inactive ? DISPATCH_QUEUE_INACTIVE : 0));
dq->dq_label = label;
dq->dq_priority = _dispatch_priority_make((dispatch_qos_t)dqai.dqai_qos,
dqai.dqai_relpri);
if (overcommit == _dispatch_queue_attr_overcommit_enabled) {
dq->dq_priority |= DISPATCH_PRIORITY_FLAG_OVERCOMMIT;
}
if (!dqai.dqai_inactive) {
_dispatch_queue_priority_inherit_from_target(dq, tq);
_dispatch_lane_inherit_wlh_from_target(dq, tq);
}
_dispatch_retain(tq);
dq->do_targetq = tq;
_dispatch_object_debug(dq, "%s", __func__);
return _dispatch_trace_queue_create(dq)._dq;
}
static inline dispatch_queue_global_t
_dispatch_get_root_queue(dispatch_qos_t qos, bool overcommit)
{
if (unlikely(qos < DISPATCH_QOS_MIN || qos > DISPATCH_QOS_MAX)) {
DISPATCH_CLIENT_CRASH(qos, "Corrupted priority");
}
return &_dispatch_root_queues[2 * (qos - 1) + overcommit];
}
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