異步改同步的場(chǎng)景
- 請(qǐng)求n個(gè)接口，幾個(gè)接口無依賴關(guān)系，在都返回?cái)?shù)據(jù)之后刷新UI或執(zhí)行其他操作
- 請(qǐng)求n個(gè)接口，幾個(gè)接口有依賴關(guān)系，在依次返回?cái)?shù)據(jù)之后刷新UI或執(zhí)行其他操作
- 一個(gè)有返回對(duì)象的方法，里邊有異步操作獲取要返回的對(duì)象或某一類型的值
場(chǎng)景一
請(qǐng)求n個(gè)接口，無依賴關(guān)系，在都返回?cái)?shù)據(jù)之后刷新UI或執(zhí)行其他操作
示例中寫了四個(gè)接口方法和一個(gè)操作方法
1. 最簡(jiǎn)單的調(diào)用方式，依次調(diào)用接口方法，在最后一個(gè)接口方法中調(diào)用刷新UI操作。
- (void)viewDidLoad {
[super viewDidLoad];
[self methodA];
}
- (void)methodA{
[self methodA:^{
[self methodB];
}];
}
- (void)methodB{
[self methodB:^{
[self methodC];
}];
}
- (void)methodC{
[self methodC:^{
[self methodD];
}];
}
- (void)methodD{
[self methodD:^{
[self method];
}];
}
- (void)methodA:(void(^)(void))success_block{
dispatch_queue_t queue = dispatch_queue_create("com.queue", DISPATCH_QUEUE_SERIAL);
dispatch_async(queue, ^{
sleep(4);
NSLog(@"執(zhí)行了方法A");
if (success_block) {
success_block();
}
});
}
- (void)methodB:(void(^)(void))success_block{
dispatch_queue_t queue = dispatch_queue_create("com.queue", DISPATCH_QUEUE_SERIAL);
dispatch_async(queue, ^{
NSLog(@"執(zhí)行了方法B");
if (success_block) {
success_block();
}
});
}
- (void)methodC:(void(^)(void))success_block{
dispatch_queue_t queue = dispatch_queue_create("com.queue", DISPATCH_QUEUE_SERIAL);
dispatch_async(queue, ^{
NSLog(@"執(zhí)行了方法C");
if (success_block) {
success_block();
}
});
}
- (void)methodD:(void(^)(void))success_block{
dispatch_queue_t queue = dispatch_queue_create("com.queue", DISPATCH_QUEUE_SERIAL);
dispatch_async(queue, ^{
NSLog(@"執(zhí)行了方法D");
if (success_block) {
success_block();
}
});
}
- (void)method{
dispatch_async(dispatch_get_main_queue(), ^{
NSLog(@"執(zhí)行了方法：刷新UI或其他操作");
});
}
執(zhí)行結(jié)果
執(zhí)行了方法A
執(zhí)行了方法B
執(zhí)行了方法C
執(zhí)行了方法D
執(zhí)行了方法：刷新UI或其他操作
2. 用dispatch_group_t 調(diào)度組 dispatch_group_enter()和dispatch_group_leave()是成對(duì)出現(xiàn)的
- (void)viewDidLoad {
[super viewDidLoad];
dispatch_group_t group = dispatch_group_create();
dispatch_queue_t queue = dispatch_queue_create("com.queue", DISPATCH_QUEUE_SERIAL);
dispatch_group_enter(group);
dispatch_group_async(group, queue, ^{
[self methodA:^{
dispatch_group_leave(group);
}];
});
dispatch_group_enter(group);
dispatch_group_async(group, queue, ^{
[self methodB:^{
dispatch_group_leave(group);
}];
});
dispatch_group_enter(group);
dispatch_group_async(group, queue, ^{
[self methodC:^{
dispatch_group_leave(group);
}];
});
dispatch_group_enter(group);
dispatch_group_async(group, queue, ^{
[self methodD:^{
dispatch_group_leave(group);
}];
});
dispatch_group_notify(group, queue, ^{
[self method];
})
}
執(zhí)行結(jié)果如下，刷新UI操作定是在最后，請(qǐng)求接口的四個(gè)方法順序不定
執(zhí)行了方法B
執(zhí)行了方法C
執(zhí)行了方法D
執(zhí)行了方法A
執(zhí)行了方法：刷新UI或其他操作
場(chǎng)景二
請(qǐng)求n個(gè)接口，幾個(gè)接口有依賴關(guān)系，在依次返回?cái)?shù)據(jù)之后刷新UI或執(zhí)行其他操作
這里假設(shè)方法A需要方法B的值 方法B需要C的值
1.可以用最簡(jiǎn)單的方式，和場(chǎng)景一的1方式一樣 直接方法套方法的去調(diào)用
2.dispatch_semaphore_t 信號(hào)量來控制請(qǐng)求順序 dispatch_semaphore_signal()信號(hào)加1 dispatch_semaphore_wait()信號(hào)減1
- (void)viewDidLoad {
[super viewDidLoad];
dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
[self methodC:^{
dispatch_semaphore_signal(semaphore);
}];
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
[self methodB:^{
dispatch_semaphore_signal(semaphore);
}];
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
[self methodA:^{
dispatch_semaphore_signal(semaphore);
}];
[self methodD:^{
dispatch_semaphore_signal(semaphore);
}];
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
[self method];
}
執(zhí)行結(jié)果
2019-02-12 11:13:32.541273+0800 GCD_Demo[91206:10764077] 執(zhí)行了方法C
2019-02-12 11:13:36.546541+0800 GCD_Demo[91206:10764077] 執(zhí)行了方法B
2019-02-12 11:13:36.546991+0800 GCD_Demo[91206:10764077] 執(zhí)行了方法A
2019-02-12 11:13:36.547034+0800 GCD_Demo[91206:10764081] 執(zhí)行了方法D
2019-02-12 11:13:36.560470+0800 GCD_Demo[91206:10764026] 執(zhí)行了方法：刷新UI或其他操作
場(chǎng)景三
一個(gè)有返回對(duì)象的方法，里邊有異步操作獲取要返回的對(duì)象或某一類型的值
1. 直接異步里邊修改局部變量
- (void)viewDidLoad {
[super viewDidLoad];
NSLog(@"%@",[self nameStr]);//是需要獲取異步得到的數(shù)值，以供同步來使用。
NSLog(@"next");
}
- (NSString *)nameStr{
__block NSString * nameStr = @"小紅";
[self method:^(NSString *name) {
nameStr = name;
}];
return nameStr;
}
- (void)method:(void(^)(NSString * name))success_block{
dispatch_queue_t queue = dispatch_queue_create("com.queue", DISPATCH_QUEUE_SERIAL);
dispatch_async(queue, ^{
if (success_block) {
success_block(@"小明");
}
});
}
運(yùn)行結(jié)果可想而知，并沒有改變局部變量
2019-02-12 11:36:45.800273+0800 GCD_Demo[92013:10799031] 小紅
2019-02-12 11:36:45.800431+0800 GCD_Demo[92013:10799031] next
2. 用while循環(huán)阻塞線程 達(dá)到異步改同步的效果
- (void)viewDidLoad {
[super viewDidLoad];
NSLog(@"%@",[self nameStr]);
NSLog(@"next");
}
- (NSString *)nameStr{
NSString __block * nameStr = @"小紅";
__block BOOL _sleep = YES;
[self method:^(NSString *name) {
nameStr = name;
NSLog(@"1");
_sleep = NO;
NSLog(@"3");
}];
while (_sleep) {
//while循環(huán)等待阻塞線程
}
NSLog(@"2");
return nameStr;
}
由打印結(jié)果可以實(shí)現(xiàn)了異步改同步
2019-02-20 09:48:39.490238+0800 GCD_Demo[12318:20531485] 1
2019-02-20 09:48:39.490351+0800 GCD_Demo[12318:20531435] 2
2019-02-20 09:48:39.490351+0800 GCD_Demo[12318:20531485] 3
2019-02-20 09:48:39.490439+0800 GCD_Demo[12318:20531435] 小明
2019-02-20 09:48:39.490501+0800 GCD_Demo[12318:20531435] next
不過，在多次運(yùn)行比較結(jié)果可知2和3的順序不定定。應(yīng)該是while循環(huán)監(jiān)聽_sleep時(shí)的機(jī)制，_sleep變量改變時(shí)while是否開始新的一次輪詢。
3. 用信號(hào)量控制 異步改同步 修改代碼如下
- (void)viewDidLoad {
[super viewDidLoad];
NSLog(@"%@",[self nameStr]);//是需要獲取異步得到的數(shù)值，以供同步來使用。
NSLog(@"next");
}
#pragma mark - 異步改同步
- (NSString *)nameStr{
__block NSString * nameStr = @"小紅";
dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
[self method:^(NSString *name) {
nameStr = name;
dispatch_semaphore_signal(semaphore);
}];
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
return nameStr;
}
運(yùn)行結(jié)果如下，block內(nèi)的修改局部變量并返回是成功的。
2019-02-12 11:34:42.340972+0800 GCD_Demo[91941:10796468] 小明
2019-02-12 11:34:42.341121+0800 GCD_Demo[91941:10796468] next
4. 利用dispatch_group_t 調(diào)度組 異步改同步 代碼如下
- (NSString *)nameStr{
__block NSString * nameStr = @"小紅";
dispatch_group_t group = dispatch_group_create();
dispatch_group_enter(group);
[self method:^(NSString *name) {
nameStr = name;
dispatch_group_leave(group);
}];
dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
return nameStr;
}
運(yùn)行結(jié)果如下，block內(nèi)的修改局部變量并返回是成功的。
2019-02-12 17:26:53.044820+0800 GCD_Demo[1838:11137671] 小明
2019-02-12 17:26:53.044949+0800 GCD_Demo[1838:11137671] next
使用示例場(chǎng)景
1. AFNetworking 3.0中 AFURLSessionManager類中L645
通過引入信號(hào)量（dispatch_semaphore）的方式把NSURLSession的異步方法 getTasksWithCompletionHandler: 變成了同步方法
這里是把本來異步的getTasksWithCompletionHandler方法變成了同步的方式了，通過引入信號(hào)量的方式，等待異步方法獲取到tasks，然后再返回。
- (NSArray *)tasksForKeyPath:(NSString *)keyPath {
__block NSArray *tasks = nil;
dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
[self.session getTasksWithCompletionHandler:^(NSArray *dataTasks, NSArray *uploadTasks, NSArray *downloadTasks) {
、、、
dispatch_semaphore_signal(semaphore);
}];
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
return tasks;
}
2.MJExtension中也有應(yīng)用
+ (NSMutableArray *)mj_totalObjectsWithSelector:(SEL)selector key:(const char *)key
{
MJExtensionSemaphoreCreate
MJExtensionSemaphoreWait
NSMutableArray *array = [self classDictForKey:key][NSStringFromClass(self)];
if (array == nil) {
// 創(chuàng)建、存儲(chǔ)
[self classDictForKey:key][NSStringFromClass(self)] = array = [NSMutableArray array];
if ([self respondsToSelector:selector]) {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
NSArray *subArray = [self performSelector:selector];
#pragma clang diagnostic pop
if (subArray) {
[array addObjectsFromArray:subArray];
}
}
[self mj_enumerateAllClasses:^(__unsafe_unretained Class c, BOOL *stop) {
NSArray *subArray = objc_getAssociatedObject(c, key);
[array addObjectsFromArray:subArray];
}];
}
MJExtensionSemaphoreSignal
return array;
}
#pragma mark - 公共方法
+ (NSMutableArray *)properties
{
NSMutableArray *cachedProperties = [self propertyDictForKey:&MJCachedPropertiesKey][NSStringFromClass(self)];
if (cachedProperties == nil) {
MJExtensionSemaphoreCreate
MJExtensionSemaphoreWait
if (cachedProperties == nil) {
cachedProperties = [NSMutableArray array];
[self mj_enumerateClasses:^(__unsafe_unretained Class c, BOOL *stop) {
// 1.獲得所有的成員變量
unsigned int outCount = 0;
objc_property_t *properties = class_copyPropertyList(c, &outCount);
// 2.遍歷每一個(gè)成員變量
for (unsigned int i = 0; i<outCount; i++) {
MJProperty *property = [MJProperty cachedPropertyWithProperty:properties[i]];
、、、
}
// 3.釋放內(nèi)存
free(properties);
}];
[self propertyDictForKey:&MJCachedPropertiesKey][NSStringFromClass(self)] = cachedProperties;
}
MJExtensionSemaphoreSignal
}
return cachedProperties;
}
另外說明的是，在MJExtension中信號(hào)量不只是用來異步改同步，把信號(hào)量當(dāng)做鎖來確保線程安全也是一個(gè)應(yīng)用場(chǎng)景 這里僅僅示例兩處 如下：
- (void)setPorpertyKeys:(NSArray *)propertyKeys forClass:(Class)c
{
if (propertyKeys.count == 0) return;
NSString *key = NSStringFromClass(c);
if (!key) return;
MJExtensionSemaphoreCreate
MJExtensionSemaphoreWait
self.propertyKeysDict[key] = propertyKeys;
MJExtensionSemaphoreSignal
}
+ (void)mj_setupObjectClassInArray:(MJObjectClassInArray)objectClassInArray
{
[self mj_setupBlockReturnValue:objectClassInArray key:&MJObjectClassInArrayKey];
MJExtensionSemaphoreCreate
MJExtensionSemaphoreWait
[[self propertyDictForKey:&MJCachedPropertiesKey] removeAllObjects];
MJExtensionSemaphoreSignal
}
MJExtension 宏注釋
// 信號(hào)量
#define MJExtensionSemaphoreCreate \
static dispatch_semaphore_t signalSemaphore; \
static dispatch_once_t onceTokenSemaphore; \
dispatch_once(&onceTokenSemaphore, ^{ \
signalSemaphore = dispatch_semaphore_create(1); \
});
#define MJExtensionSemaphoreWait \
dispatch_semaphore_wait(signalSemaphore, DISPATCH_TIME_FOREVER);
#define MJExtensionSemaphoreSignal \
dispatch_semaphore_signal(signalSemaphore);
