有个功能需要同时上传N个文件。代码如下：

ApiService as = ApiManager.getApiService();
 final ExecutorService es = Executors.newFixedThreadPool(9);
                final int count = Bimp.tempSelectBitmap.size();
                final CountDownLatch finishedLatch = new CountDownLatch(count);

                final long start = System.currentTimeMillis();

                for (int k = 0; k < count; k++) {
                    final String fp = Bimp.tempSelectBitmap.get(k).getImagePath();
                    RequestBody fbody = RequestBody.create(MediaType.parse("image/*"), new File(fp));
                    as.uploadAttach(fbody)
                            .subscribeOn(Schedulers.from(es))
                            .observeOn(Schedulers.computation())
                            .subscribe(new Subscriber<UploadAttachJSON>() {

                                @Override
                                public void onCompleted() {
                                }

                                @Override
                                public void onError(Throwable e) {
                                    finishedLatch.countDown();
                                    Log.e("UPLOAD FAILED -------->", fp);
                                }

                                @Override
                                public void onNext(UploadAttachJSON uploadAttachJSON) {
                                    finishedLatch.countDown();
                                    sb.append(uploadAttachJSON.url).append(",");
                                    Log.e("UPLOADED IMAGE URL -->", uploadAttachJSON.url);

                                    h.post(new Runnable() {
                                        @Override
                                        public void run() {
                                            pd.setMessage("正在上传...  " + (count - finishedLatch.getCount()) + "/" + count);
                                        }
                                    });
                                }

                            });
                }

                try {
                    finishedLatch.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                long end = System.currentTimeMillis();
                Log.e("IMAGE UPLOAD COMPLETED", (end - start) + "");
                es.shutdown();

以上为并行的写法。从线程池中拿出N个线程来同时上传这N个文件。

串行写法：
.subscribeOn(Schedulers.io()) 或者 用Observable.merge来合并这些请求。

结果发现并行和串行所花费的时间几乎都差不多。。 是不是和android底层有关？这些网络请求其实最后都被底层给block了，然后串行出去？