Android下，rxJava+retrofit 并发上传文件和串行上传文件的效率为什么差不多？

Question

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？

Answer 1

Is there any limit to the device’s network speed?

Answer 2

There are many factors to consider
1. Own code implementation
2. Device underlying transmission implementation
3. Server code implementation for receiving data

If any part is not concurrent, the final result will not be concurrent