memalloc.sgml

开放源码实时操作系统源码.

    <refsynopsisdiv>
      <funcsynopsis>
        <funcsynopsisinfo>
#include &lt;cyg/kernel/kapi.h&gt;
        </funcsynopsisinfo>
        <funcprototype>
          <funcdef>void <function>cyg_mempool_fix_create</function></funcdef>
          <paramdef>void* <parameter>base</parameter></paramdef>
          <paramdef>cyg_uint32 <parameter>size</parameter></paramdef>
          <paramdef>cyg_uint32 <parameter>blocksize</parameter></paramdef>
          <paramdef>cyg_handle_t* <parameter>fixpool</parameter></paramdef>
          <paramdef>cyg_mempool_fix* <parameter>fix</parameter></paramdef>
        </funcprototype>
        <funcprototype>
          <funcdef>void <function>cyg_mempool_fix_delete</function></funcdef>
          <paramdef>cyg_handle_t <parameter>fixpool</parameter></paramdef>
        </funcprototype>
        <funcprototype>
          <funcdef>void* <function>cyg_mempool_fix_alloc</function></funcdef>
          <paramdef>cyg_handle_t <parameter>fixpool</parameter></paramdef>
        </funcprototype>
        <funcprototype>
          <funcdef>void* <function>cyg_mempool_fix_timed_alloc</function></funcdef>
          <paramdef>cyg_handle_t <parameter>fixpool</parameter></paramdef>
          <paramdef>cyg_tick_count_t <parameter>abstime</parameter></paramdef>
        </funcprototype>
        <funcprototype>
          <funcdef>void* <function>cyg_mempool_fix_try_alloc</function></funcdef>
          <paramdef>cyg_handle_t <parameter>fixpool</parameter></paramdef>
        </funcprototype>
        <funcprototype>
          <funcdef>void <function>cyg_mempool_fix_free</function></funcdef>
          <paramdef>cyg_handle_t <parameter>fixpool</parameter></paramdef>
          <paramdef>void* <parameter>p</parameter></paramdef>
        </funcprototype>
        <funcprototype>
          <funcdef>cyg_bool_t <function>cyg_mempool_fix_waiting</function></funcdef>
          <paramdef>cyg_handle_t <parameter>fixpool</parameter></paramdef>
        </funcprototype>
        <funcprototype>
          <funcdef>void <function>cyg_mempool_fix_get_info</function></funcdef>
          <paramdef>cyg_handle_t <parameter>fixpool</parameter></paramdef>
          <paramdef>cyg_mempool_info* <parameter>info</parameter></paramdef>
        </funcprototype>
      </funcsynopsis>
    </refsynopsisdiv>

    <refsect1 id="memalloc-fixed-description"><title>Description</title>

      <para>
      The fixed size memory pool functions are used for allocating
      blocks of the same size. The allocation and free functions are
      more efficient than the variable size pools, but are naturally
      limited to being only able to allocate blocks of a sized
      size. Before memory can be allocated the pool must first be
      created by calling
      <function>cyg_mempool_fix_create()</function>.  

      The parameter <parameter>base</parameter> is a point to the
      bottom of the memory area to be used by the pool and
      <parameter>size</parameter> is the size of the memory area in
      bytes. <parameter>blocksize</parameter> indicates the size of
      each allocation in bytes. The function also takes a pointer to a
      <structname>cyg_mempool_fix</structname> data structure which is
      typically statically allocated, and may be part of a larger data
      structure. It should be noted that some memory is take from the
      pool for book keeping purposes. If a memory pool is no longer
      required and there are not threads waiting to allocate memory
      from it, it can be destroyed with
      <function>cyg_mempool_fix_delete()</function>.  
      </para>

      <para>
      Memory can be allocated from the pool using a number of
      functions. They all take the
      paramter<parameter>fixpool</parameter>which indicates which pool
      should be used. <function>cyg_mempool_fix_alloc()</function>
      will block until the memory becomes
      available. <function>cyg_mempool_tryalloc()</function>will try
      not block if no memory is available and will return
      <literal>NULL</literal>. Otherwise a pointer to the allocated
      memory will be returned.
      <function>cyg_mempool_fix_timed_alloc()</function> will block if
      memory is not available and wait for memory to become available
      until the time<parameter>abstime</parameter> is reached. It will
      then return <literal>NULL</literal>.  </para>

      <para>
      Allocated memory can be freed using the function <function>cyg_mempool_fix_free()</function>.
      </para>
      
      <para>
      Lastly it is possible to query information about the pool using
      the function
      <function>cyg_mempool_fix_get_info()</function>. This takes a
      pointer to the structure <structname>cyg_mempool_info</structname> which is:
      <programlisting>
typedef struct {
    cyg_int32 totalmem;
    cyg_int32 freemem;
    void      *base;
    cyg_int32 size;
    cyg_int32 blocksize;
    cyg_int32 maxfree;
} cyg_mempool_info;
      </programlisting>
     </para>
   </refsect1> 
 </refentry>

 <refentry id="malloc-pools">
 
    <refmeta>
    <refentrytitle>stdlib malloc Pools</refentrytitle>
    </refmeta>

      <refnamediv>
      <refname>malloc</refname>
      <refname>calloc</refname>
      <refname>free</refname>
      <refname>realloc</refname>
      <refname>mallinfo</refname>
      <refpurpose>stdlib malloc pool</refpurpose>
      </refnamediv>

    <refsynopsisdiv>
      <funcsynopsis>
        <funcsynopsisinfo>
#include &lt;stdlib.h&gt;
        </funcsynopsisinfo>
        <funcprototype>
          <funcdef>void *<function>malloc</function></funcdef>
          <paramdef>size_t <parameter>size</parameter></paramdef>
        </funcprototype>
        <funcprototype>
          <funcdef>void *<function>calloc</function></funcdef>
          <paramdef>size_t <parameter>nmemb</parameter></paramdef>
          <paramdef>size_t <parameter>size</parameter></paramdef>
        </funcprototype>
        <funcprototype>
          <funcdef>void <function>free</function></funcdef>
          <paramdef>void *<parameter>ptr</parameter></paramdef>
        </funcprototype>
        <funcprototype>
          <funcdef>void *<function>realloc</function></funcdef>
          <paramdef>void *<parameter>ptr</parameter></paramdef>
          <paramdef>size_t <parameter>size</parameter></paramdef>
        </funcprototype>
        <funcprototype>
          <funcdef>struct mallinfo <function>mallinfo</function></funcdef>
          <void>
        </funcprototype>
       </funcsynopsis>
    </refsynopsisdiv>

    <refsect1 id="memalloc-stdlib-description"><title>Description</title>

      <para>
      eCos provides the standard library functions used for allocating
      memory from the heap. <function>malloc()</function> allocates a
      block of memory of
      <parameter>size</parameter> bytes. <function>calloc()</function>
      performs the same, but also sets the memory to zero. The
      function <function>free()</function> returns a block to the
      pool. <function>realloc</function> resizes a block of
      memory. Lastly, <function>mallinfo()</function> returns
      information about the heap, as described by the structure
      <structname>mallinfo</structname>:

      <programlisting>
struct mallinfo {
    int arena;    /* total size of memory arena */
    int ordblks;  /* number of ordinary memory blocks */
    int smblks;   /* number of small memory blocks */
    int hblks;    /* number of mmapped regions */
    int hblkhd;   /* total space in mmapped regions */
    int usmblks;  /* space used by small memory blocks */
    int fsmblks;  /* space available for small memory blocks */
    int uordblks; /* space used by ordinary memory blocks */
    int fordblks; /* space free for ordinary blocks */
    int keepcost; /* top-most, releasable (via malloc_trim) space */
    int maxfree;  /* (NON-STANDARD EXTENSION) size of largest free block */
};
      </programlisting>
     </para>
   </refsect1> 
 </refentry>
</SECT1>
</CHAPTER> 
</PART>