你使用Rxjava时，内存泄漏了吗？

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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。