(libc.info.gz) Preparing for Obstacks

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(libc.info.gz) Creating Obstacks

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(libc.info.gz) Allocation in an Obstack

 
 3.2.4.2 Preparing for Using Obstacks
 ....................................
 
 Each source file in which you plan to use the obstack functions must
 include the header file 'obstack.h', like this:
 
      #include <obstack.h>
 
    Also, if the source file uses the macro 'obstack_init', it must
 declare or define two functions or macros that will be called by the
 obstack library.  One, 'obstack_chunk_alloc', is used to allocate the
 chunks of memory into which objects are packed.  The other,
 'obstack_chunk_free', is used to return chunks when the objects in them
 are freed.  These macros should appear before any use of obstacks in the
 source file.
 
    Usually these are defined to use 'malloc' via the intermediary
 'xmalloc' ( Unconstrained Allocation).  This is done with the
 following pair of macro definitions:
 
      #define obstack_chunk_alloc xmalloc
      #define obstack_chunk_free free
 
 Though the memory you get using obstacks really comes from 'malloc',
 using obstacks is faster because 'malloc' is called less often, for
 larger blocks of memory.   Obstack Chunks, for full details.
 
    At run time, before the program can use a 'struct obstack' object as
 an obstack, it must initialize the obstack by calling 'obstack_init'.
 
  -- Function: int obstack_init (struct obstack *OBSTACK-PTR)
      Preliminary: | MT-Safe race:obstack-ptr | AS-Safe | AC-Safe mem |
       POSIX Safety Concepts.
 
      Initialize obstack OBSTACK-PTR for allocation of objects.  This
      function calls the obstack's 'obstack_chunk_alloc' function.  If
      allocation of memory fails, the function pointed to by
      'obstack_alloc_failed_handler' is called.  The 'obstack_init'
      function always returns 1 (Compatibility notice: Former versions of
      obstack returned 0 if allocation failed).
 
    Here are two examples of how to allocate the space for an obstack and
 initialize it.  First, an obstack that is a static variable:
 
      static struct obstack myobstack;
      ...
      obstack_init (&myobstack);
 
 Second, an obstack that is itself dynamically allocated:
 
      struct obstack *myobstack_ptr
        = (struct obstack *) xmalloc (sizeof (struct obstack));
 
      obstack_init (myobstack_ptr);
 
  -- Variable: obstack_alloc_failed_handler
      The value of this variable is a pointer to a function that
      'obstack' uses when 'obstack_chunk_alloc' fails to allocate memory.
      The default action is to print a message and abort.  You should
      Termination::) or 'longjmp' ( Non-Local Exits) and doesn't
      return.
 
           void my_obstack_alloc_failed (void)
           ...
           obstack_alloc_failed_handler = &my_obstack_alloc_failed;
 

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(libc.info.gz) Creating Obstacks

(libc.info.gz) Obstacks

(libc.info.gz) Allocation in an Obstack