pool: retry allocation on OutOfDiskException from Allocator

Motivation:

To reduce the number of calls to the Allocator, the
AllocatorAwareRespitoryChannel ensures a minimum allocation size.
Towards the end of the file's upload, this results in over-allocation of
capacity.  If the file size is close to the available size then the
over-allocation can lead to the upload failing, even though sufficient
space is available to accept the file.

Modification:

If the allocation fails with OutOfDiskException then retry the
allocation without the minimum allocation.

Result:

Files are accepted that would otherwise fail.

Target: master
Require-notes: no
Require-book: no
Patch: https://rb.dcache.org/r/11090/
Acked-by: Albert Rossi

modules/dcache/src/main/java/org/dcache/pool/repository/AllocatorAwareRepositoryChannel.java

@@ -189,10 +189,7 @@ private void preallocate(long pos) throws IOException {
                 checkArgument(pos >= 0);
 
                 if (pos > allocated) {
-                    long delta = Math.max(pos - allocated, SPACE_INC);
-                    LOGGER.trace("preallocate: {}", delta);
-                    allocator.allocate(delta);
-                    allocated += delta;
+                    allocated += allocate(pos - allocated);
                 }
             } catch (InterruptedException e) {
                 throw new InterruptedIOException(e.getMessage());
@@ -201,4 +198,18 @@ private void preallocate(long pos) throws IOException {
             }
         }
     }
+
+    private long allocate(long minRequired) throws InterruptedException, OutOfDiskException
+    {
+        long delta = Math.max(minRequired, SPACE_INC);
+        try {
+            allocator.allocate(delta);
+        } catch (OutOfDiskException e) {
+            // Try again, but this time with the minimum required.
+            delta = minRequired;
+            allocator.allocate(delta);
+        }
+        LOGGER.trace("preallocate: {}", delta);
+        return delta;
+    }
 }