From 7e828035d9a2238afeac10838beff2e947d899f9 Mon Sep 17 00:00:00 2001
From: Erik Schnetter <schnetter@cct.lsu.edu>
Date: Sat, 26 May 2007 19:50:00 +0000
Subject: CarpetLib: Add class mempool

A mempool (memory pool) is a large chunk of memory.  You can allocate
pieces of it.  In order to simplify things there is no way to free a
piece again.  If the mempool is destroyed, then all its memory is
freed.  This is dangerous: you have to make sure that no one continues
to use that memory afterwards.  Using a memory pool for short-lived
objects can reduce memory fragmentation.

darcs-hash:20070526195001-dae7b-b419df094d19b85dbf145debdf62da2dc57823af.gz
---
 Carpet/CarpetLib/src/mem.cc | 55 +++++++++++++++++++++++++++++++++++++++++++++
 Carpet/CarpetLib/src/mem.hh | 41 +++++++++++++++++++++++++++++++++
 2 files changed, 96 insertions(+)

diff --git a/Carpet/CarpetLib/src/mem.cc b/Carpet/CarpetLib/src/mem.cc
index a983fc497..f53a9ccd0 100644
--- a/Carpet/CarpetLib/src/mem.cc
+++ b/Carpet/CarpetLib/src/mem.cc
@@ -135,6 +135,61 @@ has_clients () const
 
 
 
+size_t const mempool::chunksize;
+size_t const mempool::align;
+
+mempool::
+mempool ()
+  : freeptr (0), freesize (0)
+{
+}
+
+mempool::
+~mempool ()
+{
+  while (not chunks.empty()) {
+    free (chunks.top());
+    chunks.pop();
+  }
+}
+
+void *
+mempool::
+alloc (size_t nbytes)
+{
+  // Take a shortcut for silly requests
+  if (nbytes == 0) return 0;
+  
+  // Round up request size
+  nbytes = (nbytes + align - 1) / align * align;
+  
+  // If there is not enough memory left, allocate a new chunk.  Ignore
+  // whatever is left in the old chunk.
+  if (nbytes > freesize) {
+    // Allocate the usual chunk size, or more if more is requested
+    freesize = max (chunksize, nbytes);
+    freeptr = malloc (freesize);
+    if (not freeptr) {
+      CCTK_VWarn (CCTK_WARN_ABORT, __LINE__, __FILE__, CCTK_THORNSTRING,
+                  "Failed to allocate %.3f MB of memory",
+                  double(freesize/1.0e6));
+    }
+    // Remember the pointer so that it can be freed
+    chunks.push (freeptr);
+  }
+  
+  // Allocate a piece from the current chunk
+  void * const ptr = freeptr;
+  assert (freesize >= nbytes);
+  freesize -= nbytes;
+  assert (freeptr);
+  freeptr = static_cast <char *> (freeptr) + nbytes;
+  
+  return ptr;
+}
+
+
+
 extern "C" void CarpetLib_printmemstats (CCTK_ARGUMENTS);
 
 void CarpetLib_printmemstats (CCTK_ARGUMENTS)
diff --git a/Carpet/CarpetLib/src/mem.hh b/Carpet/CarpetLib/src/mem.hh
index 7ccbd6d72..b38d5459b 100644
--- a/Carpet/CarpetLib/src/mem.hh
+++ b/Carpet/CarpetLib/src/mem.hh
@@ -2,6 +2,7 @@
 #define MEM_HH
 
 #include <cstdlib>
+#include <stack>
 #include <vector>
 
 using namespace std;
@@ -34,4 +35,44 @@ public:
   bool has_clients () const;
 };
 
+
+
+// A mempool (memory pool) is a large chunk of memory.  You can
+// allocate pieces of it.  In order to simplify things there is no way
+// to free a piece again.  If the mempool is destroyed, then all its
+// memory is freed.  This is dangerous: you have to make sure that no
+// one continues to use that memory afterwards.  Using a memory pool
+// for short-lived objects can reduce memory fragmentation.
+class mempool
+{
+  // The minimum chunk size which is requested via malloc.  If a
+  // larger piece is required, then a larger chunk is allocated.
+  static size_t const chunksize = 10 * 1024 * 1024;
+  // The alignment of the returned memory.  All requests are rounded
+  // up to the next multiple of this alignment.
+  static size_t const align = 32;
+  
+  // List of all allocated chunks.  When the mempool is destroyed,
+  // these pointers need to be freed.
+  stack <void *> chunks;
+  
+  // Pointer to the beginning of some unused memory
+  void * freeptr;
+  // Size of that unused memory
+  size_t freesize;
+  
+private:
+  // Forbid copying
+  mempool (mempool const &);
+public:
+  
+  // Create and destroy a memory pool
+  mempool ();
+  ~mempool ();
+  
+  // Allocate some memory and return a pointer to it.  This cannot
+  // fail.
+  void * alloc (size_t nbytes);
+};
+
 #endif  // ifndef MEM_HH
-- 
cgit v1.2.3