9a85f0782e
Add locking around waiting for initialization to finish, since calling dispatch_block_wait from multiple threads leads to undefined behavior. Initialize RTCUIApplicationStatusObserver earlier to give the initialization block more time to run on the main thread before starting to query the application state. http://www.dailymotion.com/video/x2mckmh BUG=b/65558688 Review-Url: https://codereview.webrtc.org/3009383002 Cr-Commit-Position: refs/heads/master@{#19822}
115 lines
3.9 KiB
Objective-C
115 lines
3.9 KiB
Objective-C
/*
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* Copyright 2016 The WebRTC Project Authors. All rights reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#include "RTCUIApplicationStatusObserver.h"
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#if defined(WEBRTC_IOS)
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#import <UIKit/UIKit.h>
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#include "webrtc/rtc_base/checks.h"
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@interface RTCUIApplicationStatusObserver ()
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@property(nonatomic, assign) BOOL initialized;
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@property(nonatomic, assign) UIApplicationState state;
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@end
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@implementation RTCUIApplicationStatusObserver {
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BOOL _initialized;
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dispatch_block_t _initializeBlock;
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dispatch_semaphore_t _waitForInitializeSemaphore;
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UIApplicationState _state;
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id<NSObject> _activeObserver;
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id<NSObject> _backgroundObserver;
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}
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@synthesize initialized = _initialized;
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@synthesize state = _state;
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+ (instancetype)sharedInstance {
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static id sharedInstance;
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static dispatch_once_t onceToken;
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dispatch_once(&onceToken, ^{
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sharedInstance = [[self alloc] init];
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});
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return sharedInstance;
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}
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// Method to make sure observers are added and the initialization block is
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// scheduled to run on the main queue.
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+ (void)prepareForUse {
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__unused RTCUIApplicationStatusObserver *observer = [self sharedInstance];
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}
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- (id)init {
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if (self = [super init]) {
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NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
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__weak RTCUIApplicationStatusObserver *weakSelf = self;
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_activeObserver = [center addObserverForName:UIApplicationDidBecomeActiveNotification
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object:nil
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queue:[NSOperationQueue mainQueue]
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usingBlock:^(NSNotification *note) {
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weakSelf.state =
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[UIApplication sharedApplication].applicationState;
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}];
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_backgroundObserver = [center addObserverForName:UIApplicationDidEnterBackgroundNotification
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object:nil
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queue:[NSOperationQueue mainQueue]
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usingBlock:^(NSNotification *note) {
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weakSelf.state =
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[UIApplication sharedApplication].applicationState;
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}];
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_waitForInitializeSemaphore = dispatch_semaphore_create(1);
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_initialized = NO;
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_initializeBlock = dispatch_block_create(DISPATCH_BLOCK_INHERIT_QOS_CLASS, ^{
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weakSelf.state = [UIApplication sharedApplication].applicationState;
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weakSelf.initialized = YES;
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});
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dispatch_async(dispatch_get_main_queue(), _initializeBlock);
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}
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return self;
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}
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- (void)dealloc {
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NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
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[center removeObserver:_activeObserver];
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[center removeObserver:_backgroundObserver];
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}
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- (BOOL)isApplicationActive {
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// NOTE: The function `dispatch_block_wait` can only legally be called once.
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// Because of this, if several threads call the `isApplicationActive` method before
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// the `_initializeBlock` has been executed, instead of multiple threads calling
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// `dispatch_block_wait`, the other threads need to wait for the first waiting thread
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// instead.
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if (!_initialized) {
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dispatch_semaphore_wait(_waitForInitializeSemaphore, DISPATCH_TIME_FOREVER);
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if (!_initialized) {
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long ret = dispatch_block_wait(_initializeBlock,
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dispatch_time(DISPATCH_TIME_NOW, 10.0 * NSEC_PER_SEC));
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RTC_DCHECK_EQ(ret, 0);
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}
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dispatch_semaphore_signal(_waitForInitializeSemaphore);
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}
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return _state == UIApplicationStateActive;
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}
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@end
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#endif // WEBRTC_IOS
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