bget

COS 0.0.1.rar Cos操作系统源代码

Create  a  buffer  pool  of  <len>  bytes, using the storage starting at
<buffer>.  You can call bpool() subsequently  to  contribute  additional
storage to the overall buffer pool.

        void *bget(bufsize size);

Allocate  a  buffer  of  <size>  bytes.   The  address  of the buffer is
returned, or NULL if insufficient memory was available to  allocate  the
buffer.

        void *bgetz(bufsize size);

Allocate  a  buffer  of  <size>  bytes  and clear it to all zeroes.  The
address of the buffer is returned, or NULL if  insufficient  memory  was
available to allocate the buffer.

        void *bgetr(void *buffer, bufsize newsize);

Reallocate a buffer previously allocated by bget(), changing its size to
<newsize> and  preserving  all  existing  data.   NULL  is  returned  if
insufficient memory is available to reallocate the buffer, in which case
the original buffer remains intact.

        void brel(void *buf);

Return the buffer <buf>, previously allocated by  bget(),  to  the  free
space pool.

        void bectl(int (*compact)(bufsize sizereq, int sequence),
                   void *(*acquire)(bufsize size),
                   void (*release)(void *buf),
                   bufsize pool_incr);

Expansion  control:  specify  functions  through  which  the package may
compact storage (or take other appropriate action)  when  an  allocation
request   fails,   and  optionally  automatically  acquire  storage  for
expansion blocks when necessary,  and  release  such  blocks  when  they
become  empty.   If  <compact> is non-NULL, whenever a buffer allocation
request fails, the <compact> function  will  be  called  with  arguments
specifying  the  number  of  bytes  (total buffer size, including header
overhead) required to satisfy the allocation  request,  and  a  sequence
number   indicating   the  number  of  consecutive  calls  on  <compact>
attempting to satisfy this allocation request.  The sequence number is 1
for  the  first  call  on  <compact> for a given allocation request, and
increments on subsequent calls, permitting  the  <compact>  function  to
take  increasingly  dire  measures in an attempt to free up storage.  If
the <compact> function returns a nonzero value, the  allocation  attempt
is  re-tried.   If  <compact>  returns 0 (as it must if it isn't able to
release any space or add storage to the  buffer  pool),  the  allocation
request  fails,  which  can  trigger  automatic  pool  expansion  if the
<acquire> argument is non-NULL.  At the time the <compact>  function  is
called,  the  state  of the buffer allocator is identical to that at the
moment the allocation request  was  made;  consequently,  the  <compact>
function  may call brel(), bpool(), bstats(), and/or directly manipulate
the buffer pool in any manner which would be valid were the  application
in  control.   This does not, however, relieve the <compact> function of
the need to ensure that whatever actions it takes do not  change  things
underneath  the  application  that  made  the  allocation  request.  For
example, a <compact> function that released a buffer in the  process  of
being  reallocated  with bgetr() would lead to disaster.  Implementing a
safe and effective <compact> mechanism requires  careful  design  of  an
application's  memory  architecture,  and  cannot  generally  be  easily
retrofitted into existing code.

If <acquire> is non-NULL, that  function  will  be  called  whenever  an
allocation  request  fails.   If  the  <acquire>  function  succeeds  in
allocating the requested space and returns a pointer to  the  new  area,
allocation  will  proceed  using the expanded buffer pool.  If <acquire>
cannot obtain the requested space, it should return NULL and the  entire
allocation   process   will  fail.   <pool_incr>  specifies  the  normal
expansion block  size.   Providing  an  <acquire>  function  will  cause
subsequent  bget()  requests  for buffers too large to be managed in the
linked-block scheme (in other words, larger than <pool_incr>  minus  the
buffer  overhead)  to  be  satisfied  directly by calls to the <acquire>
function.  Automatic release of empty pool blocks will occur only if all
pool blocks in the system are the size given by <pool_incr>.

        void bstats(bufsize *curalloc, bufsize *totfree,
                    bufsize *maxfree, long *nget, long *nrel);

The  amount  of  space  currently  allocated is stored into the variable
pointed to by <curalloc>.  The total free space (sum of all free  blocks
in  the  pool)  is stored into the variable pointed to by <totfree>, and
the size of the largest single block in the free space  pool  is  stored
into  the variable pointed to by <maxfree>.  The variables pointed to by
<nget>  and  <nrel>  are  filled,  respectively,  with  the  number   of
successful  (non-NULL  return)  bget()  calls  and  the number of brel()
calls.

        void bstatse(bufsize *pool_incr, long *npool,
                     long *npget, long *nprel,
                     long *ndget, long *ndrel);

Extended statistics: The expansion block size will be  stored  into  the
variable pointed to by <pool_incr>, or the negative thereof if automatic
expansion block releases are disabled.  The number of  currently  active
pool blocks will be stored into the variable pointed to by <npool>.  The
variables pointed to  by  <npget>  and  <nprel>  will  be  filled  with,
respectively,  the  number  of expansion block acquisitions and releases
which have occurred.  The variables pointed to by  <ndget>  and  <ndrel>
will be filled with the number of bget() and brel() calls, respectively,
managed through blocks directly allocated by the acquisition and release
functions.

        void bufdump(void *buf);

The buffer pointed to by <buf> is dumped on standard output.

        void bpoold(void *pool, int dumpalloc, int dumpfree);

All  buffers in the buffer pool <pool>, previously initialised by a call
on  bpool(),  are  listed  in  ascending  memory  address   order.    If
<dumpalloc> is nonzero, the contents of allocated buffers are dumped; if
<dumpfree> is nonzero, the contents of free blocks are dumped.

        int bpoolv(void *pool);

The named buffer pool, previously initialised by a  call  on  bpool(),  is
validated  for  bad  pointers,  overwritten  data,  etc.  If compiled with
NDEBUG not defined, any error generates an assertion failure.  Otherwise 1
is returned if the pool is valid, 0 if an error is found.

BGET CONFIGURATION
==================

#define TestProg    20000  /* Generate built-in test program
                              if defined.  The value specifies
                              how many buffer allocation attempts
                              the test program should make. */

#define SizeQuant   4      /* Buffer allocation size quantum:
                              all buffers allocated are a
                              multiple of this size.  This
                              MUST be a power of two. */

#define BufDump     1      /* Define this symbol to enable the
                              bpoold() function which dumps the
                              buffers in a buffer pool. */

#define BufValid    1      /* Define this symbol to enable the
                              bpoolv() function for validating
                              a buffer pool. */ 

#define DumpData    1      /* Define this symbol to enable the
                              bufdump() function which allows
                              dumping the contents of an allocated
                              or free buffer. */

#define BufStats    1      /* Define this symbol to enable the
                              bstats() function which calculates
                              the total free space in the buffer
                              pool, the largest available
                              buffer, and the total space
                              currently allocated. */

#define FreeWipe    1      /* Wipe free buffers to a guaranteed
                              pattern of garbage to trip up
                              miscreants who attempt to use
                              pointers into released buffers. */

#define BestFit     1      /* Use a best fit algorithm when
                              searching for space for an
                              allocation request.  This uses
                              memory more efficiently, but
                              allocation will be much slower. */

#define BECtl       1      /* Define this symbol to enable the
                              bectl() function for automatic
                              pool space control.  */