commons-io引起的ygc问题

今天接到任务,图片上传服务器的性能有问题,高峰期间YGC频率在2秒一次,维护应用的程序员诊断的原因是图片处理API有性能问题。
不管咋样,亲自看一把才是王道,jmap -dump出堆内存文件。
用Eclipse MAT打开一看,发现FileCleaningTracker这个对象占用了将近一半的堆内存。
查看了下代码,发现这个类是commons-io下用于追踪文件的一个方法引起的问题。方法如下:
/**
     * Track the specified file, using the provided marker, deleting the file
     * when the marker instance is garbage collected.
     * The speified deletion strategy is used.
     *
     * @param path  the full path to the file to be tracked, not null
     * @param marker  the marker object used to track the file, not null
     * @param deleteStrategy  the strategy to delete the file, null means normal
     * @throws NullPointerException if the path is null
     */
    public void track(String path, Object marker, FileDeleteStrategy deleteStrategy) {
        if (path == null) {
            throw new NullPointerException("The path must not be null");
        }
        addTracker(path, marker, deleteStrategy);
    }


/**
     * Adds a tracker to the list of trackers.
     * 
     * @param path  the full path to the file to be tracked, not null
     * @param marker  the marker object used to track the file, not null
     * @param deleteStrategy  the strategy to delete the file, null means normal
     */
    private synchronized void addTracker(String path, Object marker, FileDeleteStrategy deleteStrategy) {
        // synchronized block protects reaper
        if (exitWhenFinished) {
            throw new IllegalStateException("No new trackers can be added once exitWhenFinished() is called");
        }
        if (reaper == null) {
            reaper = new Reaper();
            reaper.start();
        }
        trackers.add(new Tracker(path, deleteStrategy, marker, q));
    }


发现每当创建文件的时候该方法都会创建一个Reaper线程,代码如下:
/**
         * Run the reaper thread that will delete files as their associated
         * marker objects are reclaimed by the garbage collector.
         */
        @Override
        public void run() {
            // thread exits when exitWhenFinished is true and there are no more tracked objects
            while (exitWhenFinished == false || trackers.size() > 0) {
                try {
                    // Wait for a tracker to remove.
                    Tracker tracker = (Tracker) q.remove(); // cannot return null
                    trackers.remove(tracker);
                    if (!tracker.delete()) {
                        deleteFailures.add(tracker.getPath());
                    }
                    tracker.clear();
                } catch (InterruptedException e) {
                    continue;
                }
            }
        }
    }

只有当主线程手动调用exitWhenFinished方法的时候,这些Reaper线程才会进行清理动作。这样在图片上传高峰期将会在内存中积累很大的垃圾数据。

解决方案:
创建临时文件之后不调用该方法,写脚本事后进行删除工作。

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