hotspot/src/share/vm/prims/jvm.cpp

*** 1,7 ****
  /*
!  * Copyright (c) 1997, 2014, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.
--- 1,7 ----
  /*
!  * Copyright (c) 1997, 2015, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.
*** 298,307 ****
--- 298,349 ----
  JVM_LEAF(jlong, JVM_NanoTime(JNIEnv *env, jclass ignored))
    JVMWrapper("JVM_NanoTime");
    return os::javaTimeNanos();
  JVM_END
  
+ // The function below is actually exposed by sun.misc.VM and not
+ // java.lang.System, but we choose to keep it here so that it stays next
+ // to JVM_CurrentTimeMillis and JVM_NanoTime
+ 
+ const jlong MAX_DIFF_SECS = 0x0100000000;   //  2^32
+ const jlong MIN_DIFF_SECS = -MAX_DIFF_SECS; // -2^32
+ 
+ JVM_LEAF(jlong, JVM_GetNanoTimeAdjustment(JNIEnv *env, jclass ignored, jlong offset_secs))
+   JVMWrapper("JVM_GetNanoTimeAdjustment");
+   jlong seconds;
+   jlong nanos;
+   
+   os::javaTimeSystemUTC(seconds, nanos);
+ 
+   // We're going to verify that the result can fit in a long. 
+   // For that we need the difference in seconds between 'seconds'
+   // and 'offset_secs' to be such that:
+   //     |seconds - offset_secs| < (2^63/10^9)
+   // We're going to approximate 10^9 ~< 2^30 (1000^3 ~< 1024^3)
+   // which makes |seconds - offset_secs| < 2^33
+   // and we will prefer +/- 2^32 as the maximum acceptable diff
+   // as 2^32 has a more natural feel than 2^33...
+   //
+   // So if |seconds - offset_secs| >= 2^32 - we return a special
+   // sentinel value (-1) which the caller should take as an 
+   // exception value indicating that the offset given to us is
+   // too far from range of the current time - leading to too big
+   // a nano adjustment. The caller is expected to recover by
+   // computing a more accurate offset and calling this method
+   // again. (For the record 2^32 secs is ~136 years, so that
+   // should rarely happen)
+   //
+   jlong diff = seconds - offset_secs;
+   if (diff >= MAX_DIFF_SECS || diff <= MIN_DIFF_SECS) {
+      return -1; // sentinel value: the offset is too far off the target
+   }
+ 
+   // return the adjustment. If you compute a time by adding
+   // this number of nanoseconds along with the number of seconds
+   // in the offset you should get the current UTC time.
+   return (diff * (jlong)1000000000) + nanos;
+ JVM_END
  
  JVM_ENTRY(void, JVM_ArrayCopy(JNIEnv *env, jclass ignored, jobject src, jint src_pos,
                                 jobject dst, jint dst_pos, jint length))
    JVMWrapper("JVM_ArrayCopy");
    // Check if we have null pointers