[英]Block I/O in InputStream's read()
I'm trying to write an algorithm, that downloads a video live stream. 我正在尝试编写一种算法,可以下载视频直播流。 Specifically, the respective stream I'm trying to fetch is based on a dynamic .m3u8 playlist file, which periodically provides URIs of new video files.
具体来说,我要提取的各个流基于动态.m3u8播放列表文件,该文件会定期提供新视频文件的URI。 The main goal is to combine those individual media files into one coherent InputStream.
主要目标是将这些单独的媒体文件组合到一个一致的InputStream中。
I actually succeeded in getting it to work: I periodically check for new media files, that appear inside the playlist, and pass their HTTP streams to a custom InputStream implementation, namely InputStreamChain . 我实际上成功地使它起作用:我定期检查播放列表中是否出现了新的媒体文件,并将它们的HTTP流传递给自定义的InputStream实现,即InputStreamChain 。 Since it's a live stream, I assume it to be endless , at least for the time being.
由于它是实时流,因此至少在目前,我认为它是无止境的 。 Ergo, I wanted my
InputStreamChain
's read()
never to send the -1. 因此,我希望我的
InputStreamChain
的read()
永远不要发送-1。 Unfortunately, it did; 不幸的是,它确实做到了。 every time when all queued media streams were consumed, the
InputStreamChain
ended. 每当所有排队的媒体流都用完时,
InputStreamChain
结束。 Instead, I wanted it to block I/O, until a new media file arrives. 相反,我希望它阻止I / O,直到出现新的媒体文件。 So, I came up with a working solution: I adjusted the
read()
method to loop until there's a new stream available (a TimerTask
will provide the new files). 因此,我想出了一个可行的解决方案:我调整了
read()
方法使其循环播放,直到有新的流可用为止( TimerTask
将提供新文件)。 In the loop, I built in a Thread.sleep()
, in order to reduce the CPU load: 在循环中,我内置了
Thread.sleep()
,以减少CPU负载:
public int read() throws IOException {
int bit = current.read();
if (bit == -1 && streams.size() > 0) {
// left out due to lacking relevance
} else if(bit == -1 && streams.size() == 0) {
while(streams.size() == 0) {
Thread.currentThread().sleep(50);
}
return read();
}
return bit;
}
Although it seems to work, I have a feeling, that I'm not doing it how I'm supposed to. 尽管它似乎可行,但是我有一种感觉,就是我没有按照我的预期去做。 I also tried using
Lock
together with Condition.await()
, but when my TimerTask
tried to trigger Condition.signal()
, it just threw a IllegalMonitorStateException
. 我还尝试将
Lock
与Condition.await()
一起使用,但是当我的TimerTask
尝试触发Condition.signal()
,它只是抛出了IllegalMonitorStateException
。
That's why I'm asking the question : 这就是为什么我问这个问题 :
In what way should I delay/block an InputStream's read()
method, especially in my scenario? 我应该以哪种方式延迟/阻止InputStream的
read()
方法,尤其是在我的场景中?
Edit: 编辑:
For the sake of completeness, I'm going to provide my failed Lock
approach, too: 为了完整起见,我还将提供失败的
Lock
方法:
private ReentrantLock ioLock;
private Condition ioCond;
private boolean waitingForStream = false;
public InputStreamChain() {
ioLock = new ReentrantLock();
ioCond = ioLock.newCondition();
}
public synchronized InputStreamChain addInputStream(final InputStream stream) {
streams.addLast(stream);
if (current == null) {
current = streams.removeFirst();
}
if(waitingForStream) {
ioCond.signal();
}
return this;
}
public int read() throws IOException {
int bit = current.read();
if (bit == -1 && streams.size() > 0) {
// do stuff
} else if(bit == -1) {
waitingForStream = true;
ioLock.lock();
try {
ioCond.await();
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
waitingForStream = false;
ioLock.unlock();
}
return read();
}
return bit;
}
Probably you are not using synchronized block. 可能您未使用同步块。 Here is an example:
这是一个例子:
class MyReader
{
public int read() throws IOException {
int bit = current.read();
if (bit == -1 && streams.size() > 0) {
// left out due to lacking relevance
} else if(bit == -1 && streams.size() == 0) {
waitForNextStream();
return read();
}
return bit;
}
private synchronized void waitForNextStream()
{
// TODO add close handling, set current here
while (streams.isEmpty())
{
wait();
}
}
public synchronized void addNextStream(InputStream is)
{
streams.add(is);
notify();
}
}
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