tmpbuf.cpp

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#define _RWSTD_LIB_SRC
 
#include "podarray.h"        // for __rw_aligned_buffer
#include <rw/_allocator.h>   // for __rw_allocate(), ...
#include <rw/_mutex.h>       // for _RWSTD_THREAD_XXX()
#include <rw/_defs.h>
 
 
_RWSTD_NAMESPACE (__rw) {
 
// make sure buffer size is greater than zero
typedef char _CharBuf [_RWSTD_TMPBUF_SIZE + !_RWSTD_TMPBUF_SIZE];
 
// use `aligned_buffer' to guarantee proper buffer alignment
static _RWSTD_THREAD __rw_aligned_buffer<_CharBuf>
__rw_buffer;
 
static _RWSTD_THREAD unsigned long
__rw_buffer_busy /* = 0 */;   // > 0 when buffer in use
 
 
// extern "C" to avoid binary incompatibility due to changes
// in function arguments (e.g., their sign)
extern "C" {
 
 
// used by std::get_temporary_buffer<>()
_RWSTD_EXPORT _RWSTD_SIZE_T
__rw_tmpbuf (void **pptr, _RWSTD_PTRDIFF_T nelems, _RWSTD_SIZE_T size)
{
    _RWSTD_ASSERT (0 != pptr);
    _RWSTD_ASSERT (0 != size);
 
    // detect overflow and fail
    _RWSTD_SIZE_T nbytes = nelems * size;
 
    if (   nelems < 0
        || nbytes / size != _RWSTD_STATIC_CAST (_RWSTD_SIZE_T, nelems)
        || nelems && nbytes / nelems != size) {
        *pptr = 0;
        return 0;
    }
 
    // implicit initialization used to prevent a g++ 2.95.2 warning on Tru64
    // sorry: semantics of inline function static data are wrong (you'll wind
    // up with multiple copies)
 
    void* const buffer = __rw_buffer._C_data ();
 
    if (*pptr == buffer) {
 
        // static buffer being returned, decrement its usage counter
        _RWSTD_THREAD_PREDECREMENT (__rw_buffer_busy, false);
 
        return 0;
    }
 
    if (*pptr) {
        // dynamically allocated buffer being returned
        __rw_deallocate (*pptr, 0);
        return 0;
    }
 
    // allocating a new buffer
 
    if (!nbytes) {
        // don't waste memory for 0-size requests
        *pptr = 0;
        return 0;
    }
 
    if (nbytes <= _RWSTD_TMPBUF_SIZE) {
 
        if (1 == _RWSTD_THREAD_PREINCREMENT (__rw_buffer_busy, false)) {
 
            *pptr = buffer;
 
            // static buffer used, its usage counter stays non-zero
            return _RWSTD_TMPBUF_SIZE / size;
        }
 
        // static buffer not used, decrement its usage counter
        _RWSTD_THREAD_PREDECREMENT (__rw_buffer_busy, false);
    }
 
    _TRY {
        *pptr = __rw_allocate (nbytes, 0);
    }
    _CATCH (...) {
        *pptr  = 0;
        nbytes = 0;
    }
 
    return nbytes / size;
}
 
}   // extern "C"
 
 
}   // namespace __rw