(r_re_alloc): Correct realloc behavior--allow shrinking

of blocks while reallocating, if shrinking by more than one page.
(relocate_blocs, resize_blocs): Added failsafe to protect future
calling of these routines when in frozen state.
(r_alloc_thaw): Added call to r_alloc_init.
(relocate_blocks, resize_bloc, r_alloc_sbrk, r_alloc_thaw): Extended
functionality to let ralloc package work in frozen state, allowing
for the existence of unused blocks.

1 files changed, 140 insertions, 26 deletions

diff --git a/src/ralloc.c b/src/ralloc.c
index d5248f2cb0a..b6fcb323395 100644
--- a/src/ralloc.c
+++ b/src/ralloc.c
@@ -166,7 +166,13 @@ static heap_ptr first_heap, last_heap;
 /* These structures are allocated in the malloc arena.
    The linked list is kept in order of increasing '.data' members.
    The data blocks abut each other; if b->next is non-nil, then
-   b->data + b->size == b->next->data.  */
+   b->data + b->size == b->next->data.  
+
+   An element with variable==NIL denotes a freed block, which has not yet
+   been collected.  They may only appear while r_alloc_freeze > 0, and will be
+   freed when the arena is thawed.  Currently, these blocs are not reusable,
+   while the arena is frozen.  Very inefficent.  */
+
 typedef struct bp
 {
   struct bp *next;
@@ -175,8 +181,7 @@ typedef struct bp
   POINTER data;
   SIZE size;
   POINTER new_data;             /* tmporarily used for relocation */
-  /* Heap this bloc is in.  */
-  struct heap *heap;
+  struct heap *heap;            /* Heap this bloc is in.  */
 } *bloc_ptr;
 
 #define NIL_BLOC ((bloc_ptr) 0)
@@ -185,6 +190,11 @@ typedef struct bp
 /* Head and tail of the list of relocatable blocs.  */
 static bloc_ptr first_bloc, last_bloc;
 
+static int use_relocatable_buffers;
+
+/* If >0, no relocation whatsoever takes place.  */
+static int r_alloc_freeze_level;
+
 
 /* Functions to get and return memory from the system.  */
 
@@ -451,6 +461,10 @@ relocate_blocs (bloc, heap, address)
 {
   register bloc_ptr b = bloc;
 
+  /* No need to ever call this if arena is frozen, bug somewhere!  */
+  if (r_alloc_freeze_level) 
+    abort();
+
   while (b)
     {
       /* If bloc B won't fit within HEAP,
@@ -473,7 +487,9 @@ relocate_blocs (bloc, heap, address)
           /* Add up the size of all the following blocs.  */
           while (tb != NIL_BLOC)
             {
-              s += tb->size;
+              if (tb->variable) 
+                s += tb->size;
+
               tb = tb->next;
             }
 
@@ -488,7 +504,8 @@ relocate_blocs (bloc, heap, address)
       /* Record the new address of this bloc
          and update where the next bloc can start.  */
       b->new_data = address;
-      address += b->size;
+      if (b->variable) 
+        address += b->size;
       b = b->next;
     }
 
@@ -602,6 +619,10 @@ resize_bloc (bloc, size)
   POINTER address;
   SIZE old_size;
 
+  /* No need to ever call this if arena is frozen, bug somewhere!  */
+  if (r_alloc_freeze_level) 
+    abort();
+
   if (bloc == NIL_BLOC || size == bloc->size)
     return 1;
 
@@ -637,19 +658,43 @@ resize_bloc (bloc, size)
     {
       for (b = last_bloc; b != bloc; b = b->prev)
         {
-          safe_bcopy (b->data, b->new_data, b->size);
-          *b->variable = b->data = b->new_data;
+          if (!b->variable)
+            {
+              b->size = 0;
+              b->data = b->new_data;
+            } 
+          else 
+            {
+              safe_bcopy (b->data, b->new_data, b->size);
+              *b->variable = b->data = b->new_data;
+            }
+        }
+      if (!bloc->variable)
+        {
+          bloc->size = 0;
+          bloc->data = bloc->new_data;
+        }
+      else
+        {
+          safe_bcopy (bloc->data, bloc->new_data, old_size);
+          bzero (bloc->new_data + old_size, size - old_size);
+          *bloc->variable = bloc->data = bloc->new_data;
         }
-      safe_bcopy (bloc->data, bloc->new_data, old_size);
-      bzero (bloc->new_data + old_size, size - old_size);
-      *bloc->variable = bloc->data = bloc->new_data;
     }
   else
     {
       for (b = bloc; b != NIL_BLOC; b = b->next)
         {
-          safe_bcopy (b->data, b->new_data, b->size);
-          *b->variable = b->data = b->new_data;
+          if (!b->variable)
+            {
+              b->size = 0;
+              b->data = b->new_data;
+            } 
+          else 
+            {
+              safe_bcopy (b->data, b->new_data, b->size);
+              *b->variable = b->data = b->new_data;
+            }
         }
     }
 
@@ -669,6 +714,12 @@ free_bloc (bloc)
 {
   heap_ptr heap = bloc->heap;
 
+  if (r_alloc_freeze_level)
+    {
+      bloc->variable = (POINTER *) NIL;
+      return;
+    }
+  
   resize_bloc (bloc, 0);
 
   if (bloc == first_bloc && bloc == last_bloc)
@@ -713,9 +764,6 @@ free_bloc (bloc)
 
 /* Interface routines.  */
 
-static int use_relocatable_buffers;
-static int r_alloc_freeze_level;
-
 /* Obtain SIZE bytes of storage from the free pool, or the system, as
    necessary.  If relocatable blocs are in use, this means relocating
    them.  This function gets plugged into the GNU malloc's __morecore
@@ -768,7 +816,7 @@ r_alloc_sbrk (size)
         {
           get += extra_bytes + page_size;
 
-          if (r_alloc_freeze_level > 0 || ! obtain (address, get))
+          if (! obtain (address, get))
             return 0;
 
           if (first_heap == last_heap)
@@ -782,9 +830,16 @@ r_alloc_sbrk (size)
 
       if (first_heap->bloc_start < new_bloc_start)
         {
+          /* This is no clean solution - no idea how to do it better.  */
+          if (r_alloc_freeze_level) 
+            return NIL;
+
+          /* There is a bug here: if the above obtain call succeeded, but the
+             relocate_blocs call below does not succeed, we need to free
+             the memory that we got with obtain.  */
+
           /* Move all blocs upward.  */
-          if (r_alloc_freeze_level > 0
-              || ! relocate_blocs (first_bloc, h, new_bloc_start))
+          if (! relocate_blocs (first_bloc, h, new_bloc_start))
             return 0;
 
           /* Note that (POINTER)(h+1) <= new_bloc_start since
@@ -800,7 +855,6 @@ r_alloc_sbrk (size)
 
           update_heap_bloc_correspondence (first_bloc, h);
         }
-
       if (h != first_heap)
         {
           /* Give up managing heaps below the one the new
@@ -865,6 +919,10 @@ r_alloc_sbrk (size)
    the data is returned in *PTR.  PTR is thus the address of some variable
    which will use the data area.
 
+   The allocation of 0 bytes is valid.
+   In case r_alloc_freeze is set, a best fit of unused blocs could be done
+   before allocating a new area.  Not yet done.
+
    If we can't allocate the necessary memory, set *PTR to zero, and
    return zero.  */
 
@@ -919,6 +977,10 @@ r_alloc_free (ptr)
    SIZE is less than or equal to the current bloc size, in which case
    do nothing.
 
+   In case r_alloc_freeze is set, a new bloc is allocated, and the
+   memory copied to it.  Not very efficent.  We could traverse the
+   bloc_list for a best fit of free blocs first.
+
    Change *PTR to reflect the new bloc, and return this value.
 
    If more memory cannot be allocated, then leave *PTR unchanged, and
@@ -934,17 +996,51 @@ r_re_alloc (ptr, size)
   if (! r_alloc_initialized)
     r_alloc_init ();
 
+  if (!*ptr)
+    return r_alloc (ptr, size);
+  if (!size) 
+    {
+      r_alloc_free (ptr);
+      return r_alloc (ptr, 0);
+    }
+
   bloc = find_bloc (ptr);
   if (bloc == NIL_BLOC)
     abort ();
 
-  if (size <= bloc->size)
-    /* Wouldn't it be useful to actually resize the bloc here?  */
-    return *ptr;
-
-  if (! resize_bloc (bloc, MEM_ROUNDUP (size)))
-    return 0;
-
+  if (size < bloc->size) 
+    {
+      /* Wouldn't it be useful to actually resize the bloc here?  */
+      /* I think so too, but not if it's too expensive...  */
+      if ((bloc->size - MEM_ROUNDUP (size) >= page_size) 
+          && r_alloc_freeze_level == 0) 
+        {
+          resize_bloc (bloc, MEM_ROUNDUP (size));
+          /* Never mind if this fails, just do nothing...  */
+          /* It *should* be infallible!  */
+        }
+    }
+  else if (size > bloc->size)
+    {
+      if (r_alloc_freeze_level)
+        {
+          bloc_ptr new_bloc;
+          new_bloc = get_bloc (MEM_ROUNDUP (size));
+          if (new_bloc)
+            {
+              new_bloc->variable = ptr;
+              *ptr = new_bloc->data;
+              bloc->variable = (POINTER *) NIL;
+            }
+          else
+            return NIL;
+        }
+      else 
+        {
+          if (! resize_bloc (bloc, MEM_ROUNDUP (size)))
+            return NIL;
+        }
+    }
   return *ptr;
 }
 
@@ -974,9 +1070,27 @@ r_alloc_freeze (size)
 void
 r_alloc_thaw ()
 {
+
+  if (! r_alloc_initialized) 
+    r_alloc_init ();
+
   if (--r_alloc_freeze_level < 0)
     abort ();
+
+  /* This frees all unused blocs.  It is not too inefficent, as the resize 
+     and bcopy is done only once.  Afterwards, all unreferenced blocs are 
+     already shrunk to zero size.  */
+  if (!r_alloc_freeze_level) 
+    {
+      bloc_ptr *b = &first_bloc;
+      while (*b) 
+        if (!(*b)->variable) 
+          free_bloc (*b); 
+        else 
+          b = &(*b)->next;
+    }
 }
+
 
 /* The hook `malloc' uses for the function which gets more space
    from the system.  */