Sources/SPTPersistentCacheGarbageCollector.m

/*
 Copyright (c) 2015-2021 Spotify AB.

 Licensed to the Apache Software Foundation (ASF) under one
 or more contributor license agreements.  See the NOTICE file
 distributed with this work for additional information
 regarding copyright ownership.  The ASF licenses this file
 to you under the Apache License, Version 2.0 (the
 "License"); you may not use this file except in compliance
 with the License.  You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing,
 software distributed under the License is distributed on an
 "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 KIND, either express or implied.  See the License for the
 specific language governing permissions and limitations
 under the License.
 */
#import "SPTPersistentCacheGarbageCollector.h"
#import "SPTPersistentCacheDebugUtilities.h"
#import "SPTPersistentCache+Private.h"

static BOOL SPTPersistentCacheGarbageCollectorSchedulerIsInMainQueue(void);

static const NSTimeInterval SPTPersistentCacheGarbageCollectorSchedulerTimerTolerance = 300;

@interface SPTPersistentCacheGarbageCollector ()
@property (nonatomic, strong) NSTimer *timer;
@property (nonatomic, copy) SPTPersistentCacheOptions *options;
@end


@implementation SPTPersistentCacheGarbageCollector

#pragma mark - Initializer

- (instancetype)initWithCache:(SPTPersistentCache *)cache
                      options:(SPTPersistentCacheOptions *)options
                        queue:(NSOperationQueue *)queue
{
    self = [super init];
    if (self) {
        _options = [options copy];
        _cache = cache;
        _queue = queue;
    }
    return self;
}

- (void)dealloc
{
    /**
     Intentionally Left Blank

     Our timer should be invalidated by unscheduling this garbage collector
     on the -dealloc method of the object owning the reference.
     */
}

#pragma mark -

- (void)enqueueGarbageCollection:(NSTimer *)timer
{
    __weak __typeof(self) const weakSelf = self;
    NSBlockOperation *operation = [NSBlockOperation blockOperationWithBlock:^{
        // We want to shadow `self` in this case.
        _Pragma("clang diagnostic push");
        _Pragma("clang diagnostic ignored \"-Wshadow\"");
        __typeof(weakSelf) const self = weakSelf;
        _Pragma("clang diagnostic pop");

        SPTPersistentCache * const cache = self.cache;

        [cache runRegularGC];
        [cache pruneBySize];
    }];
    operation.queuePriority = self.options.garbageCollectionPriority;
    operation.qualityOfService = self.options.garbageCollectionQualityOfService;
    [self.queue addOperation:operation];
}

- (void)schedule
{
    if (!SPTPersistentCacheGarbageCollectorSchedulerIsInMainQueue()) {
        dispatch_async(dispatch_get_main_queue(), ^{
            [self schedule];
        });
        
        return;
    }
                       
    SPTPersistentCacheSafeDebugCallback([NSString stringWithFormat:@"runGarbageCollector:%@", self.timer],
                                        self.options.debugOutput);
    
    if (self.isGarbageCollectionScheduled) {
        return;
    }

    self.timer = [NSTimer timerWithTimeInterval:self.options.garbageCollectionInterval
                                         target:self
                                       selector:@selector(enqueueGarbageCollection:)
                                       userInfo:nil
                                        repeats:YES];
    
    self.timer.tolerance = SPTPersistentCacheGarbageCollectorSchedulerTimerTolerance;
    
    [[NSRunLoop mainRunLoop] addTimer:self.timer forMode:NSDefaultRunLoopMode];
}

- (void)unschedule
{
    if (!SPTPersistentCacheGarbageCollectorSchedulerIsInMainQueue()) {
        dispatch_async(dispatch_get_main_queue(), ^{
            [self unschedule];
        });
        
        return;
    }
    
    SPTPersistentCacheSafeDebugCallback([NSString stringWithFormat:@"stopGarbageCollector:%@", self.timer],
                                        self.options.debugOutput);
    
    [self.timer invalidate];
    
    self.timer = nil;
}

- (BOOL)isGarbageCollectionScheduled
{
    return (self.timer != nil);
}
@end

static BOOL SPTPersistentCacheGarbageCollectorSchedulerIsInMainQueue(void)
{
    NSString *currentQueueLabelString = [NSString stringWithUTF8String:dispatch_queue_get_label(DISPATCH_CURRENT_QUEUE_LABEL)];
    NSString *mainQueueLabelString = [NSString stringWithUTF8String:dispatch_queue_get_label(dispatch_get_main_queue())];
    return [currentQueueLabelString isEqualToString:mainQueueLabelString];
}