NSCache-apple/swift-corelibs-fou

• apple/swift-corelibs-foundation源码搜索NSCache
• 来到NSCache.h

    open func setObject(_ obj: ObjectType, forKey key: KeyType, cost g: Int) {
        let g = max(g, 0)
        let keyRef = NSCacheKey(key)
        
        _lock.lock()
        
        let costDiff: Int
        
        if let entry = _entries[keyRef] {
            costDiff = g - entry.cost
            entry.cost = g
            
            entry.value = obj
            
            if costDiff != 0 {
                remove(entry)
                insert(entry)
            }
        } else {
            let entry = NSCacheEntry(key: key, value: obj, cost: g)
            _entries[keyRef] = entry
            insert(entry)
            
            costDiff = g
        }
        
        _totalCost += costDiff
        
        var purgeAmount = (totalCostLimit > 0) ? (_totalCost - totalCostLimit) : 0
        while purgeAmount > 0 {
            if let entry = _head {
                delegate?.cache(unsafeDowncast(self, to:NSCache<AnyObject, AnyObject>.self), willEvictObject: entry.value)
                
                _totalCost -= entry.cost
                purgeAmount -= entry.cost
                
                remove(entry) // _head will be changed to next entry in remove(_:)
                _entries[NSCacheKey(entry.key)] = nil
            } else {
                break
            }
        }
        
        var purgeCount = (countLimit > 0) ? (_entries.count - countLimit) : 0
        while purgeCount > 0 {
            if let entry = _head {
                delegate?.cache(unsafeDowncast(self, to:NSCache<AnyObject, AnyObject>.self), willEvictObject: entry.value)
                
                _totalCost -= entry.cost
                purgeCount -= 1
                
                remove(entry) // _head will be changed to next entry in remove(_:)
                _entries[NSCacheKey(entry.key)] = nil
            } else {
                break
            }
        }
        
        _lock.unlock()
    }

详细略 哈哈😄