8273526: Extend the OSContainer API pids controller with pids.current

Reviewed-by: sgehwolf, iklam

src/java.base/linux/classes/jdk/internal/platform/CgroupMetrics.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, Red Hat Inc.
+ * Copyright (c) 2020, 2021, Red Hat Inc.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -154,6 +154,11 @@ public class CgroupMetrics implements Metrics {
         return subsystem.getPidsMax();
     }
 
+    @Override
+    public long getPidsCurrent() {
+        return subsystem.getPidsCurrent();
+    }
+
     @Override
     public long getBlkIOServiceCount() {
         return subsystem.getBlkIOServiceCount();

src/java.base/linux/classes/jdk/internal/platform/cgroupv1/CgroupV1Subsystem.java

@@ -416,6 +416,10 @@ public class CgroupV1Subsystem implements CgroupSubsystem, CgroupV1Metrics {
         return CgroupSubsystem.limitFromString(pidsMaxStr);
     }
 
+    public long getPidsCurrent() {
+        return getLongValue(pids, "pids.current");
+    }
+
     /*****************************************************************
      * BlKIO Subsystem
      ****************************************************************/

src/java.base/linux/classes/jdk/internal/platform/cgroupv2/CgroupV2Subsystem.java

@@ -311,6 +311,11 @@ public class CgroupV2Subsystem implements CgroupSubsystem {
         return CgroupSubsystem.limitFromString(pidsMaxStr);
     }
 
+    @Override
+    public long getPidsCurrent() {
+        return getLongVal("pids.current");
+    }
+
     @Override
     public long getBlkIOServiceCount() {
         return sumTokensIOStat(CgroupV2Subsystem::lineToRandWIOs);