Parser 中GCD的使用（6）

PFFileController 文件控制器，上传，下载，缓存文件控制。

// 串行队列， 下载，文件访问
_downloadDataAccessQueue = dispatch_queue_create("com.parse.fileController.download", DISPATCH_QUEUE_SERIAL);
    _fileStagingControllerAccessQueue = dispatch_queue_create("com.parse.filestaging.controller.access", DISPATCH_QUEUE_SERIAL);

// 串行访问
- (PFFileStagingController *)fileStagingController {
    __block PFFileStagingController *result = nil;
    dispatch_sync(_fileStagingControllerAccessQueue, ^{
        if (!self->_fileStagingController) {
            self->_fileStagingController = [PFFileStagingController controllerWithDataSource:self.dataSource];
        }
        result = self->_fileStagingController;
    });
    return result;
}

// async to UI线程， other sync excute block
- (PFProgressBlock)_fileDownloadUnifyingProgressBlockForFileState:(PFFileState *)fileState {
    return ^(int progress) {
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            __block NSArray *blocks = nil;
            dispatch_sync(self->_downloadDataAccessQueue, ^{
                blocks = [self->_downloadProgressBlocks[fileState.secureURLString] copy];
            });
            if (blocks.count != 0) {
                dispatch_async(dispatch_get_main_queue(), ^{
                    for (PFProgressBlock block in blocks) {
                        block(progress);
                    }
                });
            }
        });
    };
}

// dispatch_barrier_async 与 dispatch_async 是一样的， 串行线程
- (void)_addFileDownloadProgressBlock:(PFProgressBlock)block forFileWithState:(PFFileState *)state {
    if (!block) {
        return;
    }

    dispatch_barrier_async(self->_downloadDataAccessQueue, ^{
        NSMutableArray *progressBlocks = self->_downloadProgressBlocks[state.secureURLString];
        if (!progressBlocks) {
            progressBlocks = [NSMutableArray arrayWithObject:block];
            self->_downloadProgressBlocks[state.secureURLString] = progressBlocks;
        } else {
            [progressBlocks addObject:block];
        }
    });
}

同步队列，只是线程安全使用。

PFConfigController 配置管理

// 串行队列
_dataAccessQueue = dispatch_queue_create("com.parse.config.access", DISPATCH_QUEUE_SERIAL);

    _networkQueue = dispatch_queue_create("com.parse.config.network", DISPATCH_QUEUE_SERIAL);

// 同步 write
- (PFCurrentConfigController *)currentConfigController {
    __block PFCurrentConfigController *controller = nil;
    dispatch_sync(_dataAccessQueue, ^{
        if (!self->_currentConfigController) {
            self->_currentConfigController = [[PFCurrentConfigController alloc] initWithDataSource:self.dataSource];
        }
        controller = self->_currentConfigController;
    });
    return controller;
}

总结：串行队列，安全读写，设定 __block 来设置变量。

PFApplication 只是保证在主线程执行，有线程切换尽量选择 async

- (void)setIconBadgeNumber:(NSInteger)iconBadgeNumber {
    if (self.iconBadgeNumber != iconBadgeNumber) {
#if TARGET_OS_IOS || TARGET_OS_TV
        _iconBadgeNumber = iconBadgeNumber;
        dispatch_block_t block = ^{
            if (@available(iOS 1.0, tvOS 10.0, *)) {
                self.systemApplication.applicationIconBadgeNumber = iconBadgeNumber;
            }
        };
        if ([NSThread currentThread].isMainThread) {
            block();
        } else {
            dispatch_async(dispatch_get_main_queue(), block);
        }
#elif PF_TARGET_OS_OSX
        [[NSApplication sharedApplication] dockTile].badgeLabel = [@(iconBadgeNumber) stringValue];
#endif
    }
}

PFKeychainStore 串行线程，保证安全

PFCurrentInstallationController

// 并行队列
    _dataQueue = dispatch_queue_create("com.parse.installation.current", DISPATCH_QUEUE_CONCURRENT);


// dispatch_barrier_sync 同步 读唯一
- (BFTask *)clearCurrentInstallationAsync {
    @weakify(self);
    return [_dataTaskQueue enqueue:^BFTask *(BFTask *unused) {
        @strongify(self);

        dispatch_barrier_sync(self->_dataQueue, ^{
            self->_currentInstallation = nil;
            self->_currentInstallationMatchesDisk = NO;
        });

        ...

        return [BFTask taskForCompletionOfAllTasks:tasks];
    }];
}

- (void)setCurrentInstallation:(PFInstallation *)currentInstallation {
    dispatch_barrier_sync(_dataQueue, ^{
        if (self->_currentInstallation != currentInstallation) {
            self->_currentInstallation = currentInstallation;
        }
    });
}

// 同步都并行队列执行
- (PFInstallation *)currentInstallation {
    __block PFInstallation *installation = nil;
    dispatch_sync(_dataQueue, ^{
        installation = self->_currentInstallation;
    });
    return installation;
}