From 3396a03818a5c4e86236f91afb9158061cfcc7e2 Mon Sep 17 00:00:00 2001
From: Alexandre Duret-Lutz <adl@lrde.epita.fr>
Date: Sun, 3 Apr 2011 19:05:11 +0200
Subject: [PATCH] Add a fixed-size memory pool implementation.

* src/misc/fixpool.hh: New file.
* src/misc/Makefile.am (misc_HEADERS): Add fixpool.hh.
---
 ChangeLog            |   7 +++
 src/misc/Makefile.am |   1 +
 src/misc/fixpool.hh  | 116 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 124 insertions(+)
 create mode 100644 src/misc/fixpool.hh

diff --git a/ChangeLog b/ChangeLog
index 601b1800e..87397312d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2011-04-03  Alexandre Duret-Lutz  <adl@lrde.epita.fr>
+
+	Add a fixed-size memory pool implementation.
+
+	* src/misc/fixpool.hh: New file.
+	* src/misc/Makefile.am (misc_HEADERS): Add fixpool.hh.
+
 2011-04-03  Alexandre Duret-Lutz  <adl@lrde.epita.fr>
 
 	* HACKING (command): Some notes about link-time optimizations.
diff --git a/src/misc/Makefile.am b/src/misc/Makefile.am
index 93c2834af..d62b31fb7 100644
--- a/src/misc/Makefile.am
+++ b/src/misc/Makefile.am
@@ -33,6 +33,7 @@ misc_HEADERS = \
   bddop.hh \
   casts.hh \
   escape.hh \
+  fixpool.hh \
   freelist.hh \
   hash.hh \
   hashfunc.hh \
diff --git a/src/misc/fixpool.hh b/src/misc/fixpool.hh
new file mode 100644
index 000000000..dd8fae356
--- /dev/null
+++ b/src/misc/fixpool.hh
@@ -0,0 +1,116 @@
+// Copyright (C) 2011 Laboratoire de Recherche et Developpement de
+// l'Epita (LRDE)
+//
+// This file is part of Spot, a model checking library.
+//
+// Spot is free software; you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 2 of the License, or
+// (at your option) any later version.
+//
+// Spot 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 for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Spot; see the file COPYING.  If not, write to the Free
+// Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+// 02111-1307, USA.
+
+#ifndef SPOT_MISC_FIXPOOL_HH
+#  define SPOT_MISC_FIXPOOL_HH
+
+#include <new>
+#include <cstddef>
+#include <cstdlib>
+#include <cassert>
+
+namespace spot
+{
+
+  /// A fixed-size memory pool implementation.
+  class fixed_size_pool
+  {
+  public:
+    /// Create a pool allocating objects of \a size bytes.
+    fixed_size_pool(size_t size)
+      : freelist_(0), free_start_(0), free_end_(0), chunklist_(0)
+    {
+      const size_t alignement = 2 * sizeof(size_t);
+      size_ = ((size >= sizeof(block_) ? size : sizeof(block_))
+	       + alignement - 1) & ~(alignement - 1);
+    }
+
+    /// Free any memory allocated by this pool.
+    ~fixed_size_pool()
+    {
+      while (chunklist_)
+	{
+	  chunk_* prev = chunklist_->prev;
+	  free(chunklist_);
+	  chunklist_ = prev;
+	}
+    }
+
+    /// Allocate \a size bytes of memory.
+    void*
+    allocate()
+    {
+      block_* f = freelist_;
+      // If we have free blocks available, return the first one.
+      if (f)
+	{
+	  freelist_ = f->next;
+	  return f;
+	}
+
+      // Else, create a block out of the last chunk of allocated
+      // memory.
+
+      // If all the last chunk has been used, allocate one more.
+      if (free_start_ + size_ > free_end_)
+	{
+	  const size_t requested = (size_ > 128 ? size_ : 128) * 8192 - 64;
+	  chunk_* c = reinterpret_cast<chunk_*>(malloc(requested));
+	  if (!c)
+	    throw std::bad_alloc();
+	  c->prev = chunklist_;
+	  chunklist_ = c;
+
+	  free_start_ = c->data_ + size_;
+	  free_end_ = c->data_ + requested;
+	}
+
+      void* res = free_start_;
+      free_start_ += size_;
+      return res;
+    }
+
+    /// \brief Recycle \a size bytes of memory.
+    ///
+    /// Despite the name, the memory is not really deallocate in the
+    /// "delete" sense: it is still owned by the pool and will be
+    /// reused by allocate as soon as possible.  The memory is only
+    /// freed when the pool is destroyed.
+    void
+    deallocate (const void* ptr)
+    {
+      assert(ptr);
+      block_* b = reinterpret_cast<block_*>(const_cast<void*>(ptr));
+      b->next = freelist_;
+      freelist_ = b;
+    }
+
+  private:
+    size_t size_;
+    struct block_ { block_* next; }* freelist_;
+    char* free_start_;
+    char* free_end_;
+    // chunk = several agglomerated blocks
+    union chunk_ { chunk_* prev; char data_[1]; }* chunklist_;
+  };
+
+}
+
+#endif // SPOT_MISC_FIXPOOL_HH