你使用Rxjava时，内存泄漏了吗？

2016-07-13 本文已影响7036人 brzhang

今天有位同学问了我一个问题，话说，问我

“有遇到网络请求一半，退出Activity造成的Theard泄露吗？已在销毁时调用了un了

我去查看了下rx的源码的unsubscribe方法，定位到一个实现类，NewThreadWorker的unsubscribe方法中，源码如下：

@Override
    public void unsubscribe() {
        isUnsubscribed = true;
        executor.shutdownNow();
        deregisterExecutor(executor);
    }

    @Override
    public boolean isUnsubscribed() {
        return isUnsubscribed;
    }

这个shutdownNow()在java的注释中写的很清楚

There are no guarantees beyond best-effort attempts to stop* processing actively executing tasks.

public interface ExecutorService extends Executor {

    /**
     * Initiates an orderly shutdown in which previously submitted
     * tasks are executed, but no new tasks will be accepted.
     * Invocation has no additional effect if already shut down.
     *
     * <p>This method does not wait for previously submitted tasks to
     * complete execution.  Use {@link #awaitTermination awaitTermination}
     * to do that.
     */
    void shutdown();

    /**
     * Attempts to stop all actively executing tasks, halts the
     * processing of waiting tasks, and returns a list of the tasks
     * that were awaiting execution.
     *
     * <p>This method does not wait for actively executing tasks to
     * terminate.  Use {@link #awaitTermination awaitTermination} to
     * do that.
     *
     * <p>There are no guarantees beyond best-effort attempts to stop
     * processing actively executing tasks.  For example, typical
     * implementations will cancel via {@link Thread#interrupt}, so any
     * task that fails to respond to interrupts may never terminate.
     *
     * @return list of tasks that never commenced execution
     */
    List<Runnable> shutdownNow();

它只是尽量保证停止所有tasks，因为，如果耗时操作没有做完，finished掉activity，同时unsubscribe 掉Subscription的话，可能还有后台线程在做一些耗时任务。那么会不会造成内存泄露呢？

我觉得还是要源码来说说话吧

 /**
     * Unsubscribe from all of the subscriptions in the list, which stops the receipt of notifications on
     * the associated {@code Subscriber}.
     */
    @Override
    public void unsubscribe() {
        if (!unsubscribed) {
            List<Subscription> list;
            synchronized (this) {
                if (unsubscribed) {
                    return;
                }
                unsubscribed = true;
                list = subscriptions;
                subscriptions = null;
            }
            // we will only get here once
            unsubscribeFromAll(list);
        }
    }

    private static void unsubscribeFromAll(Collection<Subscription> subscriptions) {
        if (subscriptions == null) {
            return;
        }
        List<Throwable> es = null;
        for (Subscription s : subscriptions) {
            try {
                s.unsubscribe();
            } catch (Throwable e) {
                if (es == null) {
                    es = new ArrayList<Throwable>();
                }
                es.add(e);
            }
        }
        Exceptions.throwIfAny(es);
    }

实际上会做一些清除引用，暂停任务的操作。因此，一般来讲在activity的ondestroy中调用unsubscribe之后，是不会造成内存泄露的。但是真的是这样的吗？让我们来做做实验吧，结果说明一切。

为了能够更好的证明这一点，我还特意做了一个app demo去验证。

主要代码：

secondActivity.png

耗时任务rx封装

demo地址已经放到了github上:

内存泄露分析

启动app，首先进入的是MainActivity,然后，我们进入SecondActivity这时候，onresume执行，我们的任务也就开始了，稍微过几秒，我们退出SecondActivity，回到MainActivity，这之后，显然，SecondActivity的ondestory方法会被执行，我们可以发现日志也停止了打印。

耗时任务正在执行

如上图所示，停留在了5就不在执行了。

这时候，我们GC一下，在导出hprof文件，注意，为什么要手动GC一下呢？因为android虚拟机去GC也是有策略的，有GC周期的。这时候可能并没有GC过，也就是说，SecondActivity的内存可能并没有被释放，但并不等于说，SecondActivity就泄露了，因为他也有可能是可以被GC的，只是还没有来得及被GC而已。总之，在导出hprof文件之前，最好先手动GC一下。就是下图那个车子，嗯，点一下吧，放心点。