mirror of https://github.com/oxen-io/session-ios
Merge branch 'charlesmchen/attachmentDownloadsVsBackground'
Matthew Chen
8 years ago
commit
40ec869072
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//
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// Copyright (c) 2017 Open Whisper Systems. All rights reserved.
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//
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typedef NS_ENUM(NSUInteger, BackgroundTaskState) {
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BackgroundTaskState_Success,
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BackgroundTaskState_CouldNotStart,
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BackgroundTaskState_Expired,
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};
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typedef void (^BackgroundTaskCompletionBlock)(BackgroundTaskState backgroundTaskState);
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// This class makes it easier and safer to use background tasks.
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//
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// * Uses RAII (Resource Acquisition Is Initialization) pattern.
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// * Ensures completion block is called exactly once and on main thread,
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// to facilitate handling "background task timed out" case, for example.
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// * Ensures we properly handle the "background task could not be created"
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// case.
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//
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// Usage:
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//
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// * Use factory method to start a background task.
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// * Retain a strong reference to the OWSBackgroundTask during the "work".
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// * Clear all references to the OWSBackgroundTask when the work is done,
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// if possible.
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@interface OWSBackgroundTask : NSObject
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- (instancetype)init NS_UNAVAILABLE;
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+ (OWSBackgroundTask *)backgroundTaskWithLabelStr:(const char *)labelStr;
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// completionBlock will be called exactly once on the main thread.
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+ (OWSBackgroundTask *)backgroundTaskWithLabelStr:(const char *)labelStr
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completionBlock:(BackgroundTaskCompletionBlock)completionBlock;
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+ (OWSBackgroundTask *)backgroundTaskWithLabel:(NSString *)label;
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// completionBlock will be called exactly once on the main thread.
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+ (OWSBackgroundTask *)backgroundTaskWithLabel:(NSString *)label
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completionBlock:(BackgroundTaskCompletionBlock)completionBlock;
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@end
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//
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// Copyright (c) 2017 Open Whisper Systems. All rights reserved.
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//
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#import "OWSBackgroundTask.h"
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#import "AppContext.h"
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#import "Threading.h"
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@interface OWSBackgroundTask ()
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@property (nonatomic, readonly) NSString *label;
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// This property should only be accessed while synchronized on this instance.
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@property (nonatomic) UIBackgroundTaskIdentifier backgroundTaskId;
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// This property should only be accessed while synchronized on this instance.
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@property (nonatomic, nullable) BackgroundTaskCompletionBlock completionBlock;
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@end
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#pragma mark -
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@implementation OWSBackgroundTask
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+ (OWSBackgroundTask *)backgroundTaskWithLabelStr:(const char *)labelStr
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{
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OWSAssert(labelStr);
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NSString *label = [NSString stringWithFormat:@"%s", labelStr];
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return [[OWSBackgroundTask alloc] initWithLabel:label completionBlock:nil];
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}
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+ (OWSBackgroundTask *)backgroundTaskWithLabelStr:(const char *)labelStr
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completionBlock:(BackgroundTaskCompletionBlock)completionBlock
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{
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OWSAssert(labelStr);
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NSString *label = [NSString stringWithFormat:@"%s", labelStr];
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return [[OWSBackgroundTask alloc] initWithLabel:label completionBlock:completionBlock];
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}
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+ (OWSBackgroundTask *)backgroundTaskWithLabel:(NSString *)label
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{
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return [[OWSBackgroundTask alloc] initWithLabel:label completionBlock:nil];
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}
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+ (OWSBackgroundTask *)backgroundTaskWithLabel:(NSString *)label
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completionBlock:(BackgroundTaskCompletionBlock)completionBlock
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{
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return [[OWSBackgroundTask alloc] initWithLabel:label completionBlock:completionBlock];
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}
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- (instancetype)initWithLabel:(NSString *)label completionBlock:(BackgroundTaskCompletionBlock _Nullable)completionBlock
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{
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self = [super init];
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if (!self) {
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return self;
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}
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OWSAssert(label.length > 0);
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_label = label;
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self.completionBlock = completionBlock;
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[self startBackgroundTask];
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return self;
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}
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- (void)dealloc
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{
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[self endBackgroundTask];
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}
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- (void)startBackgroundTask
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{
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// beginBackgroundTaskWithExpirationHandler must be called on the main thread.
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DispatchMainThreadSafe(^{
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__weak typeof(self) weakSelf = self;
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self.backgroundTaskId = [CurrentAppContext() beginBackgroundTaskWithExpirationHandler:^{
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// Note the usage of OWSCAssert() to avoid capturing a reference to self.
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OWSCAssert([NSThread isMainThread]);
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OWSBackgroundTask *strongSelf = weakSelf;
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if (!strongSelf) {
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return;
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}
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// Make a local copy of completionBlock to ensure that it is called
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// exactly once.
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BackgroundTaskCompletionBlock _Nullable completionBlock = nil;
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@synchronized(strongSelf)
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{
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if (strongSelf.backgroundTaskId == UIBackgroundTaskInvalid) {
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return;
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}
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DDLogInfo(@"%@ %@ background task expired.", strongSelf.logTag, strongSelf.label);
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strongSelf.backgroundTaskId = UIBackgroundTaskInvalid;
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completionBlock = strongSelf.completionBlock;
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strongSelf.completionBlock = nil;
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}
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if (completionBlock) {
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completionBlock(BackgroundTaskState_Expired);
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}
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}];
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// If a background task could not be begun, call the completion block.
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if (self.backgroundTaskId == UIBackgroundTaskInvalid) {
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DDLogInfo(@"%@ %@ background task could not be started.", self.logTag, self.label);
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// Make a local copy of completionBlock to ensure that it is called
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// exactly once.
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BackgroundTaskCompletionBlock _Nullable completionBlock;
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@synchronized(self)
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{
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completionBlock = self.completionBlock;
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self.completionBlock = nil;
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}
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if (completionBlock) {
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completionBlock(BackgroundTaskState_CouldNotStart);
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}
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}
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});
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}
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- (void)endBackgroundTask
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{
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// Make a local copy of this state, since this method is called by `dealloc`.
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UIBackgroundTaskIdentifier backgroundTaskId;
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BackgroundTaskCompletionBlock _Nullable completionBlock;
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NSString *logTag = self.logTag;
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NSString *label = self.label;
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@synchronized(self)
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{
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backgroundTaskId = self.backgroundTaskId;
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completionBlock = self.completionBlock;
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self.completionBlock = nil;
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}
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if (backgroundTaskId == UIBackgroundTaskInvalid) {
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OWSAssert(!completionBlock);
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return;
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}
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// endBackgroundTask must be called on the main thread.
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DispatchMainThreadSafe(^{
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DDLogVerbose(@"%@ %@ background task completed.", logTag, label);
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if (completionBlock) {
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completionBlock(BackgroundTaskState_Success);
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}
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[CurrentAppContext() endBackgroundTask:backgroundTaskId];
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});
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}
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@end
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