1 files changed, 77 insertions, 0 deletions
diff --git a/src/inc/iallocator.h b/src/inc/iallocator.h
new file mode 100644
index 0000000000..b4c1b71120
--- /dev/null
+++ b/src/inc/iallocator.h
@@ -0,0 +1,77 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+// We would like to allow "util" collection classes to be usable both
+// from the VM and from the JIT.  The latter case presents a
+// difficulty, because in the (x86, soon to be cross-platform) JIT
+// compiler, we require allocation to be done using a "no-release"
+// (aka, arena-style) allocator that is provided as methods of the
+// JIT's Compiler type.
+
+// To allow utilcode collection classes to deal with this, they may be
+// written to do allocation and freeing via an instance of the
+// "IAllocator" class defined in this file.  
+// 
+#ifndef _IALLOCATOR_DEFINED_
+#define _IALLOCATOR_DEFINED_
+
+#include "contract.h"
+#include "safemath.h"
+
+class IAllocator
+{
+  public:
+    virtual void* Alloc(size_t sz) = 0;
+
+    // Allocate space for an array of "elems" elements, each of size "elemSize".
+    virtual void* ArrayAlloc(size_t elems, size_t elemSize) = 0;
+
+    virtual void  Free(void* p) = 0;
+};
+
+// This class wraps an allocator that does not allow zero-length allocations,
+// producing one that does (every zero-length allocation produces a pointer to the same
+// statically-allocated memory, and freeing that pointer is a no-op).
+class AllowZeroAllocator: public IAllocator
+{
+    int m_zeroLenAllocTarg;
+    IAllocator* m_alloc;
+
+public:
+    AllowZeroAllocator(IAllocator* alloc) : m_alloc(alloc) {}
+
+    void* Alloc(size_t sz)
+    {
+        if (sz == 0)
+        {
+            return (void*)(&m_zeroLenAllocTarg);
+        }
+        else
+        {
+            return m_alloc->Alloc(sz);
+        }
+    }
+
+    void* ArrayAlloc(size_t elemSize, size_t numElems)
+    {
+        if (elemSize == 0 || numElems == 0)
+        {
+            return (void*)(&m_zeroLenAllocTarg);
+        }
+        else
+        {
+            return m_alloc->ArrayAlloc(elemSize, numElems);
+        }
+    }
+
+    virtual void Free(void * p)
+    {
+        if (p != (void*)(&m_zeroLenAllocTarg))
+        {
+            m_alloc->Free(p);
+        }
+    }
+};
+
+#endif // _IALLOCATOR_DEFINED_