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iOS多线程GCD 研究
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Grand Central Dispatch (GCD)是Apple開發的一個多核編程的解決方法。
Java代碼 ?
__OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_4_0)?? DISPATCH_EXPORT?struct?dispatch_queue_s?_dispatch_main_q;?? #define?dispatch_get_main_queue()?\?? DISPATCH_GLOBAL_OBJECT(dispatch_queue_t,?_dispatch_main_q)?? /*!
* @function dispatch_get_main_queue
*
* @abstract
* Returns the default queue that is bound to the main thread.
*
* @discussion
* In order to invoke blocks submitted to the main queue, the application must
* call dispatch_main(), NSApplicationMain(), or use a CFRunLoop on the main
* thread.
*
* @result
* Returns the main queue. This queue is created automatically on behalf of
* the main thread before main() is called.
*/
__OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_4_0)
DISPATCH_EXPORT struct dispatch_queue_s _dispatch_main_q;
#define dispatch_get_main_queue() \
DISPATCH_GLOBAL_OBJECT(dispatch_queue_t, _dispatch_main_q)
可以看出，dispatch_get_main_queue也是一種dispatch_queue_t。
Java代碼 ?
?dispatch_async(dispatch_get_global_queue(0,?0),?^{?? ?????? ?});?? ?? ? ?dispatch_async(dispatch_get_main_queue(),?^{?? ?????? ?});?? ?? ? ?static?dispatch_once_t?onceToken;?? ?dispatch_once(&onceToken,?^{?? ????? ?});?? ?? ? ?double?delayInSeconds?=?2.0;?? ?dispatch_time_t?popTime?=?dispatch_time(DISPATCH_TIME_NOW,?delayInSeconds?*?NSEC_PER_SEC);?? ?dispatch_after(popTime,?dispatch_get_main_queue(),?^(void){?? ????? ?});?? ?? ? ?dispatch_queue_t?urls_queue?=?dispatch_queue_create("blog.devtang.com",?NULL);?? ?dispatch_async(urls_queue,?^{???? ? ?});?? ?dispatch_release(urls_queue);?? ?? ? ?dispatch_group_t?group?=?dispatch_group_create();?? ?dispatch_group_async(group,?dispatch_get_global_queue(0,0),?^{?? ?????? ?});?? ?dispatch_group_async(group,?dispatch_get_global_queue(0,0),?^{?? ?????? ?});?? ?dispatch_group_notify(group,?dispatch_get_global_queue(0,0),?^{?? ?????? ?});?? // 后臺執行：dispatch_async(dispatch_get_global_queue(0, 0), ^{// something});// 主線程執行：dispatch_async(dispatch_get_main_queue(), ^{// something});// 一次性執行：static dispatch_once_t onceToken;dispatch_once(&onceToken, ^{// code to be executed once});// 延遲2秒執行：double delayInSeconds = 2.0;dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);dispatch_after(popTime, dispatch_get_main_queue(), ^(void){// code to be executed on the main queue after delay});// 自定義dispatch_queue_tdispatch_queue_t urls_queue = dispatch_queue_create("blog.devtang.com", NULL);dispatch_async(urls_queue, ^{ // your code });dispatch_release(urls_queue);// 合并匯總結果dispatch_group_t group = dispatch_group_create();dispatch_group_async(group, dispatch_get_global_queue(0,0), ^{// 并行執行的線程一});dispatch_group_async(group, dispatch_get_global_queue(0,0), ^{// 并行執行的線程二});dispatch_group_notify(group, dispatch_get_global_queue(0,0), ^{// 匯總結果});
一個應用GCD的例子：
Java代碼 ?
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,?0),?^{?? ????????NSURL?*?url?=?[NSURL?URLWithString:@"http://www.baidu.com"];?? ????????NSError?*?error;?? ????????NSString?*?data?=?[NSString?stringWithContentsOfURL:url?encoding:NSUTF8StringEncoding?error:&error];?? ????????if?(data?!=?nil)?{?? ????????????dispatch_async(dispatch_get_main_queue(),?^{?? ????????????????NSLog(@"call?back,?the?data?is:?%@",?data);?? ????????????});?? ????????}?else?{?? ????????????NSLog(@"error?when?download:%@",?error);?? ????????}?? ????});?? dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{NSURL * url = [NSURL URLWithString:@"http://www.baidu.com"];NSError * error;NSString * data = [NSString stringWithContentsOfURL:url encoding:NSUTF8StringEncoding error:&error];if (data != nil) {dispatch_async(dispatch_get_main_queue(), ^{NSLog(@"call back, the data is: %@", data);});} else {NSLog(@"error when download:%@", error);}});
GCD的另一個用處是可以讓程序在后臺較長久的運行。
Java代碼 ?
@property?(assign,?nonatomic)?UIBackgroundTaskIdentifier?backgroundUpdateTask;?? ?? -?(void)applicationDidEnterBackground:(UIApplication?*)application?? {?? ????[self?beingBackgroundUpdateTask];?? ???? ????[self?endBackgroundUpdateTask];?? }?? ?? -?(void)beingBackgroundUpdateTask?? {?? ????self.backgroundUpdateTask?=?[[UIApplication?sharedApplication]?beginBackgroundTaskWithExpirationHandler:^{?? ????????[self?endBackgroundUpdateTask];?? ????}];?? }?? ?? -?(void)endBackgroundUpdateTask?? {?? ????[[UIApplication?sharedApplication]?endBackgroundTask:?self.backgroundUpdateTask];?? ????self.backgroundUpdateTask?=?UIBackgroundTaskInvalid;?? }??
轉載于:https://www.cnblogs.com/lovewx/p/4042202.html
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