src/share/classes/java/nio/Bits.java

@@ -24,10 +24,15 @@
  */
 
 package java.nio;
 
 import java.security.AccessController;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.atomic.LongAdder;
+
+import sun.misc.JavaLangRefAccess;
+import sun.misc.SharedSecrets;
 import sun.misc.Unsafe;
 import sun.misc.VM;
 
 /**
  * Access to bits, native and otherwise.

@@ -619,59 +624,107 @@
 
     // A user-settable upper limit on the maximum amount of allocatable
     // direct buffer memory.  This value may be changed during VM
     // initialization if it is launched with "-XX:MaxDirectMemorySize=<size>".
     private static volatile long maxMemory = VM.maxDirectMemory();
-    private static volatile long reservedMemory;
-    private static volatile long totalCapacity;
-    private static volatile long count;
-    private static boolean memoryLimitSet = false;
+    private static final AtomicLong reservedMemory = new AtomicLong();
+    private static final AtomicLong totalCapacity = new AtomicLong();
+    private static final AtomicLong count = new AtomicLong();
+    private static volatile boolean memoryLimitSet = false;
+    // max. number of sleeps during try-reserving with exponentially
+    // increasing delay before throwing OutOfMemoryError:
+    // 1, 2, 4, 8, 16, 32, 64, 128, 256 (total 511 ms ~ 0.5 s)
+    // which means that OOME will be thrown after 0.5 s of trying
+    private static final int MAX_SLEEPS = 9;
 
     // These methods should be called whenever direct memory is allocated or
     // freed.  They allow the user to control the amount of direct memory
     // which a process may access.  All sizes are specified in bytes.
     static void reserveMemory(long size, int cap) {
-        synchronized (Bits.class) {
+
             if (!memoryLimitSet && VM.isBooted()) {
                 maxMemory = VM.maxDirectMemory();
                 memoryLimitSet = true;
             }
-            // -XX:MaxDirectMemorySize limits the total capacity rather than the
-            // actual memory usage, which will differ when buffers are page
-            // aligned.
-            if (cap <= maxMemory - totalCapacity) {
-                reservedMemory += size;
-                totalCapacity += cap;
-                count++;
+
+        // optimist!
+        if (tryReserveMemory(size, cap)) {
+            return;
+        }
+
+        final JavaLangRefAccess jlra = SharedSecrets.getJavaLangRefAccess();
+
+        // retry while helping enqueue pending Reference objects
+        // which includes executing pending Cleaner(s) which includes
+        // Cleaner(s) that free direct buffer memory
+        while (jlra.tryHandlePendingReference()) {
+            if (tryReserveMemory(size, cap)) {
                 return;
             }
         }
 
+        // trigger VM's Reference processing
         System.gc();
+
+        // a retry loop with exponential back-off delays
+        // (this gives VM some time to do it's job)
+        boolean interrupted = false;
         try {
-            Thread.sleep(100);
-        } catch (InterruptedException x) {
-            // Restore interrupt status
-            Thread.currentThread().interrupt();
+            long sleepTime = 1;
+            int sleeps = 0;
+            while (true) {
+                if (tryReserveMemory(size, cap)) {
+                    return;
+                }
+                if (sleeps >= MAX_SLEEPS) {
+                    break;
+                }
+                if (!jlra.tryHandlePendingReference()) {
+                    try {
+                        Thread.sleep(sleepTime);
+                        sleepTime <<= 1;
+                        sleeps++;
+                    } catch (InterruptedException e) {
+                        interrupted = true;
         }
-        synchronized (Bits.class) {
-            if (totalCapacity + cap > maxMemory)
+                }
+            }
+
+            // no luck
                 throw new OutOfMemoryError("Direct buffer memory");
-            reservedMemory += size;
-            totalCapacity += cap;
-            count++;
+
+        } finally {
+            if (interrupted) {
+                // don't swallow interrupts
+                Thread.currentThread().interrupt();
+            }
+        }
         }
 
+    private static boolean tryReserveMemory(long size, int cap) {
+
+        // -XX:MaxDirectMemorySize limits the total capacity rather than the
+        // actual memory usage, which will differ when buffers are page
+        // aligned.
+        long totalCap;
+        while (cap <= maxMemory - (totalCap = totalCapacity.get())) {
+            if (totalCapacity.compareAndSet(totalCap, totalCap + cap)) {
+                reservedMemory.addAndGet(size);
+                count.incrementAndGet();
+                return true;
+            }
     }
 
-    static synchronized void unreserveMemory(long size, int cap) {
-        if (reservedMemory > 0) {
-            reservedMemory -= size;
-            totalCapacity -= cap;
-            count--;
-            assert (reservedMemory > -1);
+        return false;
         }
+
+
+    static void unreserveMemory(long size, int cap) {
+        long cnt = count.decrementAndGet();
+        long reservedMem = reservedMemory.addAndGet(-size);
+        long totalCap = totalCapacity.addAndGet(-cap);
+        assert cnt >= 0 && reservedMem >= 0 && totalCap >= 0;
     }
 
     // -- Monitoring of direct buffer usage --
 
     static {

@@ -685,19 +738,19 @@
                         public String getName() {
                             return "direct";
                         }
                         @Override
                         public long getCount() {
-                            return Bits.count;
+                            return Bits.count.get();
                         }
                         @Override
                         public long getTotalCapacity() {
-                            return Bits.totalCapacity;
+                            return Bits.totalCapacity.get();
                         }
                         @Override
                         public long getMemoryUsed() {
-                            return Bits.reservedMemory;
+                            return Bits.reservedMemory.get();
                         }
                     };
                 }
                 @Override
                 public ByteBuffer newDirectByteBuffer(long addr, int cap, Object ob) {