--- old/src/java.base/share/classes/java/lang/ProcessBuilder.java	2019-07-19 13:42:21.926172540 -0700
+++ new/src/java.base/share/classes/java/lang/ProcessBuilder.java	2019-07-19 13:42:21.490172431 -0700
@@ -25,6 +25,8 @@
 
 package java.lang;
 
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.VarHandle;
 import java.io.File;
 import java.io.FileDescriptor;
 import java.io.IOException;
@@ -209,7 +211,7 @@
     public ProcessBuilder(List<String> command) {
         if (command == null)
             throw new NullPointerException();
-        this.command = command;
+        COMMAND.setRelease(this, command);
     }
 
     /**
@@ -224,9 +226,10 @@
      * @param command a string array containing the program and its arguments
      */
     public ProcessBuilder(String... command) {
-        this.command = new ArrayList<>(command.length);
+        List<String> commandList = new ArrayList<>(command.length);
         for (String arg : command)
-            this.command.add(arg);
+            commandList.add(arg);
+        COMMAND.setRelease(this, commandList);
     }
 
     /**
@@ -243,7 +246,7 @@
     public ProcessBuilder command(List<String> command) {
         if (command == null)
             throw new NullPointerException();
-        this.command = command;
+        COMMAND.setRelease(this, command);
         return this;
     }
 
@@ -274,7 +277,7 @@
      * @return this process builder's program and its arguments
      */
     public List<String> command() {
-        return command;
+        return (List<String>) COMMAND.getAcquire(this);
     }
 
     /**
@@ -350,12 +353,15 @@
         if (security != null)
             security.checkPermission(new RuntimePermission("getenv.*"));
 
-        if (environment == null)
-            environment = ProcessEnvironment.environment();
-
-        assert environment != null;
-
-        return environment;
+        // Multiple threads may call this method without synchronization
+        for (;;) {
+            Map<String,String> environment = (Map<String,String>)
+                ENVIRONMENT.getAcquire(this);
+            if (environment != null)
+                return environment;
+            ENVIRONMENT.compareAndSet(this, null,
+                                      ProcessEnvironment.environment());
+        }
     }
 
     // Only for use by Runtime.exec(...envp...)
@@ -1298,4 +1304,19 @@
         }
         return processes;
     }
+
+    // VarHandle mechanics
+    private static final VarHandle COMMAND;
+    private static final VarHandle ENVIRONMENT;
+    static {
+        try {
+            MethodHandles.Lookup l = MethodHandles.lookup();
+            COMMAND = l.findVarHandle(
+                    ProcessBuilder.class, "command", List.class);
+            ENVIRONMENT = l.findVarHandle(
+                    ProcessBuilder.class, "environment", Map.class);
+        } catch (ReflectiveOperationException e) {
+            throw new ExceptionInInitializerError(e);
+        }
+    }
 }