--- a/hotspot/src/share/vm/memory/metaspace.cpp	Wed Oct 01 12:29:28 2014 +0400
+++ b/hotspot/src/share/vm/memory/metaspace.cpp	Wed Oct 01 16:09:01 2014 +0200
@@ -1415,10 +1415,31 @@
   return value;
 }
 
-size_t MetaspaceGC::inc_capacity_until_GC(size_t v) {
+bool MetaspaceGC::inc_capacity_until_GC(size_t v, size_t* new_cap_until_GC, size_t* old_cap_until_GC) {
   assert_is_size_aligned(v, Metaspace::commit_alignment());
 
-  return (size_t)Atomic::add_ptr(v, &_capacity_until_GC);
+  size_t capacity_until_GC = (size_t) _capacity_until_GC;
+  size_t new_value = capacity_until_GC + v;
+
+  if (new_value < capacity_until_GC) {
+    // The addition wrapped around, set new_value to aligned max value.
+    new_value = align_size_down(max_uintx, Metaspace::commit_alignment());
+  }
+
+  intptr_t expected = (intptr_t) capacity_until_GC;
+  intptr_t actual = Atomic::cmpxchg_ptr((intptr_t) new_value, &_capacity_until_GC, expected);
+
+  if (expected != actual) {
+    return false;
+  }
+
+  if (new_cap_until_GC != NULL) {
+    *new_cap_until_GC = new_value;
+  }
+  if (old_cap_until_GC != NULL) {
+    *old_cap_until_GC = capacity_until_GC;
+  }
+  return true;
 }
 
 size_t MetaspaceGC::dec_capacity_until_GC(size_t v) {
@@ -1518,7 +1539,10 @@
     expand_bytes = align_size_up(expand_bytes, Metaspace::commit_alignment());
     // Don't expand unless it's significant
     if (expand_bytes >= MinMetaspaceExpansion) {
-      size_t new_capacity_until_GC = MetaspaceGC::inc_capacity_until_GC(expand_bytes);
+      size_t new_capacity_until_GC = 0;
+      bool succeeded = MetaspaceGC::inc_capacity_until_GC(expand_bytes, &new_capacity_until_GC);
+      assert(succeeded, "Should always succesfully increment HWM when at safepoint");
+
       Metaspace::tracer()->report_gc_threshold(capacity_until_GC,
                                                new_capacity_until_GC,
                                                MetaspaceGCThresholdUpdater::ComputeNewSize);
@@ -3321,19 +3345,29 @@
   size_t delta_bytes = MetaspaceGC::delta_capacity_until_GC(word_size * BytesPerWord);
   assert(delta_bytes > 0, "Must be");
 
-  size_t after_inc = MetaspaceGC::inc_capacity_until_GC(delta_bytes);
-
-  // capacity_until_GC might be updated concurrently, must calculate previous value.
-  size_t before_inc = after_inc - delta_bytes;
-
-  tracer()->report_gc_threshold(before_inc, after_inc,
-                                MetaspaceGCThresholdUpdater::ExpandAndAllocate);
-  if (PrintGCDetails && Verbose) {
-    gclog_or_tty->print_cr("Increase capacity to GC from " SIZE_FORMAT
-        " to " SIZE_FORMAT, before_inc, after_inc);
+  size_t before = 0;
+  size_t after = 0;
+  MetaWord* res;
+  bool incremented;
+
+  // Each thread increments the HWM at most once. Even if the thread fails to increment
+  // the HWM, an allocation is still attempted. This is because another thread must then
+  // have incremented the HWM and therefore the allocation might still succeed.
+  do {
+    incremented = MetaspaceGC::inc_capacity_until_GC(delta_bytes, &after, &before);
+    res = allocate(word_size, mdtype);
+  } while (!incremented && res == NULL);
+
+  if (incremented) {
+    tracer()->report_gc_threshold(before, after,
+                                  MetaspaceGCThresholdUpdater::ExpandAndAllocate);
+    if (PrintGCDetails && Verbose) {
+      gclog_or_tty->print_cr("Increase capacity to GC from " SIZE_FORMAT
+          " to " SIZE_FORMAT, before, after);
+    }
   }
 
-  return allocate(word_size, mdtype);
+  return res;
 }
 
 // Space allocated in the Metaspace.  This may

--- a/hotspot/src/share/vm/memory/metaspace.hpp	Wed Oct 01 12:29:28 2014 +0400
+++ b/hotspot/src/share/vm/memory/metaspace.hpp	Wed Oct 01 16:09:01 2014 +0200
@@ -407,7 +407,9 @@
   static void post_initialize();
 
   static size_t capacity_until_GC();
-  static size_t inc_capacity_until_GC(size_t v);
+  static bool inc_capacity_until_GC(size_t v,
+                                    size_t* new_cap_until_GC = NULL,
+                                    size_t* old_cap_until_GC = NULL);
   static size_t dec_capacity_until_GC(size_t v);
 
   static bool should_concurrent_collect() { return _should_concurrent_collect; }

--- a/hotspot/src/share/vm/prims/whitebox.cpp	Wed Oct 01 12:29:28 2014 +0400
+++ b/hotspot/src/share/vm/prims/whitebox.cpp	Wed Oct 01 16:09:01 2014 +0200
@@ -820,6 +820,33 @@
   MetadataFactory::free_array(cld, (Array<u1>*)(uintptr_t)addr);
 WB_END
 
+WB_ENTRY(jlong, WB_IncMetaspaceCapacityUntilGC(JNIEnv* env, jobject wb, jlong inc))
+  if (inc < 0) {
+    THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(),
+        err_msg("WB_IncMetaspaceCapacityUntilGC: inc is negative: " JLONG_FORMAT, inc));
+  }
+
+  jlong max_size_t = (jlong) ((size_t) -1);
+  if (inc > max_size_t) {
+    THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(),
+        err_msg("WB_IncMetaspaceCapacityUntilGC: inc does not fit in size_t: " JLONG_FORMAT, inc));
+  }
+
+  size_t new_cap_until_GC = 0;
+  size_t aligned_inc = align_size_down((size_t) inc, Metaspace::commit_alignment());
+  bool success = MetaspaceGC::inc_capacity_until_GC(aligned_inc, &new_cap_until_GC);
+  if (!success) {
+    THROW_MSG_0(vmSymbols::java_lang_IllegalStateException(),
+                "WB_IncMetaspaceCapacityUntilGC: could not increase capacity until GC "
+                "due to contention with another thread");
+  }
+  return (jlong) new_cap_until_GC;
+WB_END
+
+WB_ENTRY(jlong, WB_MetaspaceCapacityUntilGC(JNIEnv* env, jobject wb))
+  return (jlong) MetaspaceGC::capacity_until_GC();
+WB_END
+
 //Some convenience methods to deal with objects from java
 int WhiteBox::offset_for_field(const char* field_name, oop object,
     Symbol* signature_symbol) {
@@ -991,6 +1018,8 @@
      CC"(Ljava/lang/ClassLoader;J)J",                 (void*)&WB_AllocateMetaspace },
   {CC"freeMetaspace",
      CC"(Ljava/lang/ClassLoader;JJ)V",                (void*)&WB_FreeMetaspace },
+  {CC"incMetaspaceCapacityUntilGC", CC"(J)J",         (void*)&WB_IncMetaspaceCapacityUntilGC },
+  {CC"metaspaceCapacityUntilGC", CC"()J",             (void*)&WB_MetaspaceCapacityUntilGC },
   {CC"getCPUFeatures",     CC"()Ljava/lang/String;",  (void*)&WB_GetCPUFeatures     },
   {CC"getNMethod",         CC"(Ljava/lang/reflect/Executable;Z)[Ljava/lang/Object;",
                                                       (void*)&WB_GetNMethod         },

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hotspot/test/gc/metaspace/TestCapacityUntilGCWrapAround.java	Wed Oct 01 16:09:01 2014 +0200
@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) 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.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @key gc
+ * @bug 8049831
+ * @library /testlibrary /testlibrary/whitebox
+ * @build TestCapacityUntilGCWrapAround
+ * @run main ClassFileInstaller sun.hotspot.WhiteBox
+ *                              sun.hotspot.WhiteBox$WhiteBoxPermission
+ * @run main/othervm -Xbootclasspath/a:. -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI TestCapacityUntilGCWrapAround
+ */
+
+import sun.hotspot.WhiteBox;
+
+import com.oracle.java.testlibrary.Asserts;
+import com.oracle.java.testlibrary.Platform;
+
+public class TestCapacityUntilGCWrapAround {
+    private static long MB = 1024 * 1024;
+    private static long GB = 1024 * MB;
+    private static long MAX_UINT = 4 * GB - 1; // On 32-bit platforms
+
+    public static void main(String[] args) {
+        if (Platform.is32bit()) {
+            WhiteBox wb = WhiteBox.getWhiteBox();
+
+            long before = wb.metaspaceCapacityUntilGC();
+            // Now force possible overflow of capacity_until_GC.
+            long after = wb.incMetaspaceCapacityUntilGC(MAX_UINT);
+
+            Asserts.assertGTE(after, before,
+                              "Increasing with MAX_UINT should not cause wrap around: " + after + " < " + before);
+            Asserts.assertLTE(after, MAX_UINT,
+                              "Increasing with MAX_UINT should not cause value larger than MAX_UINT:" + after);
+        }
+    }
+}

--- a/hotspot/test/testlibrary/whitebox/sun/hotspot/WhiteBox.java	Wed Oct 01 12:29:28 2014 +0400
+++ b/hotspot/test/testlibrary/whitebox/sun/hotspot/WhiteBox.java	Wed Oct 01 16:09:01 2014 +0200
@@ -152,6 +152,8 @@
   public native void readReservedMemory();
   public native long allocateMetaspace(ClassLoader classLoader, long size);
   public native void freeMetaspace(ClassLoader classLoader, long addr, long size);
+  public native long incMetaspaceCapacityUntilGC(long increment);
+  public native long metaspaceCapacityUntilGC();
 
   // force Young GC
   public native void youngGC();