Rxjava源碼分析之IO.Reactivex.CompositeDisposable

該處源碼分析是基於Rxjava3而非Rxjava2，兩者有細微的差別。
RxJava容易造成內存泄漏，在某些情況下沒有及時的取消訂閱會導致內存泄漏。CompositeDisposable就是專用於Disposable管理的。

CompositeDisposable是一個Disposable容器，它提供了多種算法時間複雜度爲O(1)的方法，如add、remove、delete等方法。實質是內部有一個OpenHashSet實例resources專用於添加移除管理Disposable。

CompositeDisposable中的主要方法

• 1、dispose() ，resources置空，並且爲逐個Dispose在resources中的每一個Disposable

• 2、add(@NonNull Disposable disposable)和addAll(@NonNull Disposable disposable)，添加Disposable或其集合到resources中，如果CompositeDisposable已經disposed，則添加的Disposable會直接dispose取消訂閱，無法執行Disposable中的任務。

• 3、remove(@NonNull Disposable disposable) 和 delete(@NonNull Disposable disposable)。remove方法實質調用了delete,且多了一步 disposable.dispose()。remove即從容器resources中不但remove,且執行完畢後該 disposable取消與訂閱者的連接關係dispose();

• 4、clear(), dispose容器resources中所包含的所有Disposable

CompositeDisposable的使用注意：

• 該類中所有需要傳Disposable的參數都不能爲null,否則拋出NullPointerException
• 一般在OnCreate中創建CompositeDisposable實例，在onDestory方法中進行clear()操作
• 爲了方便disposable 的管理，可以在Observer.onSubscribe(Disposable d)中將Disposable的實例加入CompositeDisposable中。

     .subscribe(new Observer() {
                    @Override
                    public void onSubscribe(Disposable d) {
                        if(d!=null){
                            compositeDisposable.add(d);
                        }
                    }
  

CompositeDisposable源碼如下：

public class IO_Reactivex_CompositeDisposable implements Disposable, DisposableContainer {

    /**
     * 存放 disposable 的 set
     */
    private OpenHashSet<Disposable> resources;

    /**
     * 是否已經處理過
     */
    private volatile boolean disposed;

    /**
     * Creates an empty {@code CompositeDisposable}.
     */
    public IO_Reactivex_CompositeDisposable() {
    }

    /**
     * Creates a {@code CompositeDisposable} with the given array of initial {@link Disposable} elements.
     * 創建 一個CompositeDisposable 通過給定的 初始元素數組。
     *
     * @param disposables the array of {@code Disposable}s to start with    起始的Disposables
     * @throws NullPointerException if {@code disposables} or any of its array items is {@code null} 如果存在一個disposable,則拋空異常
     */
    public IO_Reactivex_CompositeDisposable(@NonNull Disposable... disposables) {
        Objects.requireNonNull(disposables, "disposables is null");
        this.resources = new OpenHashSet<>(disposables.length + 1);
        for (Disposable d : disposables) {
            Objects.requireNonNull(d, "A Disposable in the disposables array is null");
            this.resources.add(d);
        }
    }

    /**
     * 創建 一個CompositeDisposable 通過給定的初始化元素 Iterable 序列
     * Creates a {@code CompositeDisposable} with the given {@link Iterable} sequence of initial {@link Disposable} elements.
     *
     * @param disposables the {@code Iterable} sequence of {@code Disposable} to start with   初始參數
     * @throws NullPointerException if {@code disposables} or any of its items is {@code null}   存在null 拋異常
     */
    public IO_Reactivex_CompositeDisposable(@NonNull Iterable<? extends Disposable> disposables) {
        Objects.requireNonNull(disposables, "disposables is null");
        this.resources = new OpenHashSet<>();
        for (Disposable d : disposables) {
            Objects.requireNonNull(d, "A Disposable item in the disposables sequence is null");
            this.resources.add(d);
        }
    }

    @Override
    public void dispose() {
        //已經處理過，不在調用
        if (disposed) {
            return;
        }
        OpenHashSet<Disposable> set;
        // 前面添加的OpenHashSet<Disposable> 清空，置null
        synchronized (this) {
            if (disposed) {
                return;
            }
            disposed = true;
            set = resources;
            resources = null;
        }

        dispose(set);
    }


    @Override
    public boolean isDisposed() {
        return disposed;
    }

    //TODO CompositeDisposable 的初始化，add 等方法中傳入參數Disposable 或其數組都不可爲null,否則拋空異常

    /**
     * TODO 添加一個Disposable 到 container容器中 ，如果container已經disposed,此時返回false且disposable.dispose();
     * Adds a {@link Disposable} to this container or disposes it if the
     * container has been disposed.
     *
     * @param disposable the {@code Disposable} to add, not {@code null}
     * @return {@code true} if successful, {@code false} if this container has been disposed
     * @throws NullPointerException if {@code disposable} is {@code null}
     */
    @Override
    public boolean add(@NonNull Disposable disposable) {
        Objects.requireNonNull(disposable, "disposable is null");
        if (!disposed) {
            synchronized (this) {
                if (!disposed) {
                    OpenHashSet<Disposable> set = resources;
                    // 剛剛初始化的CompositeDisposable,此時resources=null
                    if (set == null) {
                        set = new OpenHashSet<>();
                        resources = set;
                    }
                    set.add(disposable);
                    return true;
                }
            }
        }
        disposable.dispose();
        return false;
    }

    /**
     * 一次添加一個Disposable數組成功則返回true，如果容器disposed,則Disposable數組批量dispose此時返回false
     * Atomically adds the given array of {@link Disposable}s to the container or
     * disposes them all if the container has been disposed.
     *
     * @param disposables the array of {@code Disposable}s
     * @return {@code true} if the operation was successful, {@code false} if the container has been disposed
     * @throws NullPointerException if {@code disposables} or any of its array items is {@code null}
     */
    public boolean addAll(@NonNull Disposable... disposables) {
        Objects.requireNonNull(disposables, "disposables is null");
        if (!disposed) {
            synchronized (this) {
                if (!disposed) {
                    OpenHashSet<Disposable> set = resources;
                    if (set == null) {
                        set = new OpenHashSet<>(disposables.length + 1);
                        resources = set;
                    }
                    for (Disposable d : disposables) {
                        Objects.requireNonNull(d, "A Disposable in the disposables array is null");
                        set.add(d);
                    }
                    return true;
                }
            }
        }
        for (Disposable d : disposables) {
            d.dispose();
        }
        return false;
    }

    /**
     * TODO 如果disposable是resources中的一個，則從resources中移除，並且將該Disposable.dispose
     * Removes and disposes the given {@link Disposable} if it is part of this container.
     *
     * @param disposable the disposable to remove and dispose, not {@code null}
     * @return {@code true} if the operation was successful
     * @throws NullPointerException if {@code disposable} is {@code null}
     */
    @Override
    public boolean remove(@NonNull Disposable disposable) {
        if (delete(disposable)) {
            disposable.dispose();
            return true;
        }
        return false;
    }

    /**
     * TODO 從resources中移除Disposable，但不dispose。 如果resources=null，
     * TODO 或者resources.remove返回false,則該方法返回false
     * Removes (but does not dispose) the given {@link Disposable} if it is part of this container.
     *
     * @param disposable the disposable to remove, not {@code null}
     * @return {@code true} if the operation was successful
     * @throws NullPointerException if {@code disposable} is {@code null}
     */
    @Override
    public boolean delete(@NonNull Disposable disposable) {
        Objects.requireNonNull(disposable, "disposable is null");
        if (disposed) {
            return false;
        }
        synchronized (this) {
            if (disposed) {
                return false;
            }

            OpenHashSet<Disposable> set = resources;
            if (set == null || !set.remove(disposable)) {
                return false;
            }
        }
        return true;
    }

    /**
     * 原子性的清理container， 然後dispose 前面所有包含的Disposables
     * Atomically clears the container, then disposes all the previously contained {@link Disposable}s.
     */
    public void clear() {
        if (disposed) {
            return;
        }
        OpenHashSet<Disposable> set;
        synchronized (this) {
            if (disposed) {
                return;
            }

            set = resources;
            resources = null;
        }

        dispose(set);
    }

    /**
     * 返回 resources中的count
     * Returns the number of currently held {@link Disposable}s.
     *
     * @return the number of currently held {@code Disposable}s
     */
    public int size() {
        if (disposed) {
            return 0;
        }
        synchronized (this) {
            if (disposed) {
                return 0;
            }
            OpenHashSet<Disposable> set = resources;
            return set != null ? set.size() : 0;
        }
    }

    /**
     * TODO Dispose OpenHashSet中的元素 通過非致命的方式最後。  如果該過程中產生了異常，則拋出異常。
     * Dispose the contents of the {@link OpenHashSet} by suppressing non-fatal
     * {@link Throwable}s till the end.
     *
     * @param set the {@code OpenHashSet} to dispose elements of
     */
    private void dispose(@Nullable OpenHashSet<Disposable> set) {
        if (set == null) {
            return;
        }
        List<Throwable> errors = null;
        Object[] array = set.keys();
        for (Object o : array) {
            if (o instanceof Disposable) {
                try {
                    ((Disposable) o).dispose();
                } catch (Throwable ex) {
                    Exceptions.throwIfFatal(ex);
                    if (errors == null) {
                        errors = new ArrayList<>();
                    }
                    errors.add(ex);
                }
            }
        }
        if (errors != null) {
            if (errors.size() == 1) {
                throw ExceptionHelper.wrapOrThrow(errors.get(0));
            }
            throw new CompositeException(errors);
        }
    }
}

該篇博客純屬個人觀點和見解，如有錯誤懇請留言指正，萬分感激！

關聯鏈接：

• Rxjava源碼分析之IO.Reactivex.Observer