Docker中的Java 9 ProcessHandle API：PID值和可見進程的差異

Question

在簡單的「Dockerized」Java程序中嘗試使用Java 9中的新的ProcessHandle API時，發現在檢索進程ID時行爲方面存在差異正在運行的進程。特別是在調用方法ProcessHandle.pid(),時，Docker上生成的PID與主機上顯示的本機ID不同，儘管文檔說該方法「返回進程的本機進程ID」。另外，ProcessHandle.allProcesses()的結果有差異。

爲了演示，下面的程序執行以下操作：

1. 打印當前進程的PID，
2. 產生一個子進程，休眠幾秒鐘（允許時間打印的信息） ，
3. 並最終打印所有可見的進程。

---

public static void main(String[] args) { 
    System.out.println("### Current process info ###"); 
    ProcessHandle currentProcess = ProcessHandle.current(); 
    printInfo(currentProcess); 

    System.out.println(); 

    // Fork a child process that lasts for a few seconds 
    spawnProcess("jshell --startup ./sleep.txt"); 

    printAllVisibleProcesses(); 
} 

private static void printAllVisibleProcesses() { 
    System.out.println("### Visible processes info ###"); 
    ProcessHandle.allProcesses().forEach(ProcessHandleExamples::printInfo); 
    System.out.println(); 
} 

private static void spawnProcess(String command) { 
    System.out.println("Spawning: " + command); 
    try { 
     Runtime.getRuntime().exec(command); 
    } catch (IOException e) { 
     e.printStackTrace(); 
    } 
} 

private static void printInfo(ProcessHandle processHandle) { 
    ProcessHandle.Info processInfo = processHandle.info(); 
    System.out.println("Process ID: " + processHandle.pid()); 

    System.out.println("Process arguments: " + Arrays.toString(processInfo.arguments().orElse(new String[0]))); 
    System.out.println("Process executable: " + processInfo.command().orElse("")); 
    System.out.println("Process command line: " + processInfo.commandLine().orElse("")); 
    System.out.println("Process start time: " + processInfo.startInstant().orElse(null)); 
    System.out.println("Process total cputime accumulated: " + processInfo.totalCpuDuration().orElse(null)); 
    System.out.println("Process user: " + processInfo.user().orElse("")); 
} 

當正常運行的應用程序（不多克爾）時，如預期的輸出;它包含當前進程的本地PID，其子進程以及許多其他可見進程。

### Current process info ### 
Process ID: 7756 
Process arguments: [] 
Process executable: D:\Dev\Java\jdk-9\bin\java.exe 
Process command line: 
Process start time: 2017-10-08T12:23:46.474Z 
Process total cputime accumulated: PT0.4368028S 
Process user: manouti 

Spawning: jshell --startup ./sleep.txt 
### Visible processes info ### 
... skipping some output 
Process ID: 8060 
Process arguments: [] 
Process executable: C:\Program Files (x86)\Google\Chrome\Application\chrome.exe 
Process command line: 
Process start time: 2017-10-08T12:20:04.758Z 
Process total cputime accumulated: PT10.4676671S 
Process user: manouti 

Process ID: 7756 
Process arguments: [] 
Process executable: D:\Dev\Java\jdk-9\bin\java.exe 
Process command line: 
Process start time: 2017-10-08T12:23:46.474Z 
Process total cputime accumulated: PT0.8268053S 
Process user: manouti 

Process ID: 8080 
Process arguments: [] 
Process executable: D:\Dev\Java\jdk-9\bin\jshell.exe 
Process command line: 
Process start time: 2017-10-08T12:23:46.992Z 
Process total cputime accumulated: PT0.0780005S 
Process user: manouti 

當我（與上一boot2docker的Linux運行泊塢的Windows 7）上運行的泊塢窗，流程更小的子集是可見的，的PID不匹配主機上的人。

$ docker run test/java9-processhandle-example:1.0

運行上述命令後，主機顯示了以下過程：

然而，得到的程序輸出下面示出的代替的PID 1和16， 4291和4333.可見過程包括容器過程和產生的過程。

我想知道這是否是預期的。由於我對Docker相對來說比較陌生，如果這是容器造成的限制，如果有人能解釋它，我會很高興（我也不確定這是否可以在不同的Docker設置上重現，例如Linux或Windows上的Docker服務器）。否則，這是API本身在應用於容器時的限制（在Javadoc中似乎沒有提及任何內容）？

### Current process info ### 
Process ID: 1 
Process arguments: [ProcessHandleExamples] 
Process executable: /usr/lib/jvm/java-9-openjdk-amd64/bin/java 
Process command line: /usr/lib/jvm/java-9-openjdk-amd64/bin/java ProcessHandleExamples 
Process start time: 2017-10-08T14:17:48.420Z 
Process total cputime accumulated: PT0.35S 
Process user: root 

Spawning: jshell --startup ./sleep.txt 
### Visible processes info ### 
Process ID: 1 
Process arguments: [ProcessHandleExamples] 
Process executable: /usr/lib/jvm/java-9-openjdk-amd64/bin/java 
Process command line: /usr/lib/jvm/java-9-openjdk-amd64/bin/java ProcessHandleExamples 
Process start time: 2017-10-08T14:17:48.420Z 
Process total cputime accumulated: PT0.6S 
Process user: root 

Process ID: 16 
Process arguments: [--startup, ./sleep.txt] 
Process executable: /usr/lib/jvm/java-9-openjdk-amd64/bin/jshell 
Process command line: /usr/lib/jvm/java-9-openjdk-amd64/bin/jshell --startup ./sleep.txt 
Process start time: 2017-10-08T14:17:49.070Z 
Process total cputime accumulated: PT0.03S 
Process user: root 

Answer 1

這不是特定於Java或Java 9，它是一個碼頭主題。

每個容器都有自己的PID命名空間和在該容器中運行的第一個進程有1

您可以在docker documentation閱讀更多關於這一點，特別是PID：

通過默認情況下，所有容器都啓用了PID名稱空間。

PID名稱空間提供進程分離。的PID命名空間移除系統進程的視圖，並允許過程ID，以包括PID被重用1.

Answer 2

所以運行的容器--pid=host需要以允許如所暗示的ProcessHandle.pid()返回預期值文檔（由操作系統分配的本地PID）。

它也使得ProcessHandle.allProcesses()返回系統可見進程，而不僅僅是綁定到容器的進程。