Question

我正在Linux上使用OpenJDK 11，我需要确保使用HttpURLConnection完成的所有Web请求均已正确关闭，并且不保持任何文件描述符打开。

Oracle's manual告诉在close上使用InputStream，而Android's manual告诉在disconnect对象上使用HttpURLConnection。

我还将Connection: close和http.keepAlive设置为false以避免连接池。

这似乎适用于普通的 http 请求，但不适用于使用非分块编码发送的加密的 https 请求。似乎只有GC可以清理关闭的连接。

此示例代码：

import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.stream.Stream;

public class Test {
    private static int printFds() throws IOException {
        int cnt = 0;
        try (Stream<Path> paths = Files.list(new File("/proc/self/fd").toPath())) {
            for (Path path : (Iterable<Path>)paths::iterator) {
                System.out.println(path);
                ++cnt;
            }
        }
        System.out.println();
        return cnt;
    }

    public static void main(String[] args) throws IOException, InterruptedException {
        System.setProperty("http.keepAlive", "false");
        for (int i = 0; i < 10; i++) {
            // Must be a https endpoint returning non-chunked response
            HttpURLConnection conn = (HttpURLConnection) new URL("https://www.google.com/").openConnection();
            conn.setRequestProperty("Connection", "close");
            BufferedReader in = new BufferedReader(new InputStreamReader(conn.getInputStream()));
            while (in.readLine() != null) {
            }
            in.close();
            conn.disconnect();
            conn = null;
            in = null;
        }

        Thread.sleep(1000);
        int numBeforeGc = printFds();

        System.gc();
        Thread.sleep(1000);
        int numAfterGc = printFds();
        System.out.println(numBeforeGc == numAfterGc ? "No socket leaks" : "Sockets were leaked");
    }
}

打印此输出：

/proc/self/fd/0
/proc/self/fd/1
/proc/self/fd/2
/proc/self/fd/3
/proc/self/fd/4
/proc/self/fd/5
/proc/self/fd/9
/proc/self/fd/6
/proc/self/fd/7
/proc/self/fd/8
/proc/self/fd/10
/proc/self/fd/11
/proc/self/fd/12
/proc/self/fd/13
/proc/self/fd/14
/proc/self/fd/15
/proc/self/fd/16
/proc/self/fd/17
/proc/self/fd/18
/proc/self/fd/19

/proc/self/fd/0
/proc/self/fd/1
/proc/self/fd/2
/proc/self/fd/3
/proc/self/fd/4
/proc/self/fd/5
/proc/self/fd/9
/proc/self/fd/6
/proc/self/fd/7
/proc/self/fd/8

Sockets were leaked

更改为http URL会使套接字在没有GC的情况下按预期正确关闭：

/proc/self/fd/0
/proc/self/fd/1
/proc/self/fd/2
/proc/self/fd/3
/proc/self/fd/4
/proc/self/fd/5
/proc/self/fd/6

/proc/self/fd/0
/proc/self/fd/1
/proc/self/fd/2
/proc/self/fd/3
/proc/self/fd/4
/proc/self/fd/5
/proc/self/fd/6

No socket leak

已经通过OpenJDK 11和12进行了测试。我错过了什么吗？或者这是一个错误吗？

Answer 1

原来毕竟是一个错误：https://bugs.openjdk.java.net/browse/JDK-8216326

shutdownInput现在在最新版本的JDK 11和13（但不是12）中由close取代。

HttpURLConnection的套接字泄漏

1 个答案: