我正在Linux上使用OpenJDK 11,并且需要确保所有通过HttpURLConnection完成的Web请求都被正确关闭,并且不保留任何文件描述符。Oracle的手册建议在
打印以下输出:
InputStream
上使用close
,而Android的手册则建议在HttpURLConnection
对象上使用disconnect
。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,但不适用于响应发送了非分块编码的加密HTTPS请求。只有进行垃圾回收才能清除已关闭的连接。以下是示例代码: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");
}
}
打印以下输出:
/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
将URL改为HTTP后,套接字会按预期正确关闭,而不会触发垃圾回收:
/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
已测试使用OpenJDK 11和12。我有什么遗漏或这是一个错误吗?
shutdown(fd,SHUT_RD)
,但没有close
(直到GC)。 - Emil