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<title>PTypes: Portability and Performance Issues</title>
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<p><a href="../index.html"><img src="title-21.png" width="253" height="39" alt="C++ Portable Types Library (PTypes) Version 2.1" border="0"></a>
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<p class="hpath"><a href="index.html">Top</a>: Portability and performance issues</p>
<p><br>
<b> 64-bit integers</b>: most compilers provide <span class="lang">long long</span>
type modifier for declaring 64-bit integers, but at least two of them, Microsoft
C/C++ and Borland C/C++, use quite unaesthetic keyword <span class="lang">__int64</span>.
PTypes offers its own wrapper type <span class="lang">large</span> (in <a href="include/pport.h.html"><pport.h></a>),
which is a portable signed 64-bit integer. <span class="lang">Unsigned large</span>
or <span class="lang">ularge</span> are also available. For portable 64-bit string
conversions use <span class="lang">itostring()</span> and <span class="lang">stringto*()</span>
declared in <a href="include/ptypes.h.html"><ptypes.h></a>.</p>
<p>Another incompatibility exists for printf-style formatted output routines:
Windows uses "I64" type modifier for 64-bit integers, whereas standard-compliant
libraries recognize "ll" (ell-ell). PTypes solves this problem in its
<span class="lang">outstm::putf()</span> method: you can safely use "ll"
modifier on all platforms.</p>
<p><b>End-of-line sequences</b>: PTypes input stream routines automatically recognize
three types of EOL sequences: LF (UNIX), CR (Mac) and CR-LF (DOS/Win) and set
<span class="lang">instm::eol</span> property accordingly.</p>
<p>As for output streams, unlike many Windows-based C run-time libraries, PTypes
does NOT make any translations and always sends your data as is. In order to generate
an EOL sequence appropriate to the target platform (i.e. the system your application
is running on), use <span class="lang">outstm::puteol()</span> and <span class="lang">outstm::putline(string)</span>.
Some protocols and data formats, however, require some predetermined EOL sequence
regardless of the target platform, e.g. HTTP always uses CR-LF, PostScript uses
CR, etc. In such cases you can use standard C escape sequences to send appropriate
codes to the output stream, e.g. "\r\n" or "\r".</p>
<p><b>File names</b>: you can always use UNIX-style path names (with slash '/')
when working with files through PTypes streaming classes. Since drive specifiers
in path names are specific only to Windows, try to use relative paths in your
program whenever possible. For additional notes on pipe naming, please see introduction
for the <a href="streams.namedpipe.html">namedpipe</a> class.</p>
<p><b>Arithmetic operations and multithreading</b>: a simple increment and decrement
operation (i++ and i--) in a multithreaded application may NOT be thread-safe
on most RISC CPU's and on i386-based multiprocessor systems. Even if you are not
interested in the resulting value of an increment/decrement operation, still use
PTypes <span class="lang">pincrement()</span> and <span class="lang">pdecrement()</span>
on variables shared between threads.</p>
<p><b>Performance of dynamic strings</b>: most of the string operations rely on
dynamic memory reallocation. PTypes tries to avoid frequent use of physical reallocation
by aligning the dynamic string buffers on 16, 32, 64 ... 4096-byte boundaries,
depending on the logical size of a string. Physical reallocation highly depends
on the performance of the standard <span class="lang">realloc()</span> function,
which may vary from OS to OS. Linux, for example, performs reallocations up to
30 times faster than Windows on a similar computer. PTypes dynamic strings also
depend on the performance of the atomic increment and decrement functions (see
below).</p>
<p><b>Performance of atomic increment/decrement/exchange operations</b>: on SPARC, PowerPC
and i386-based platforms PTypes implements atomic operations using CPU instructions. On all other platforms these operations use slower mutex
locking (see <span class="lang">src/patomic.cxx</span>).</p>
<p><b>Reentrancy of synchronization objects</b>: the POSIX standard does not specify
whether synchronization objects should be reentrant or not. For instance, if you
use recursive locks on a mutex object the behaviour of your application may vary
on different systems. Most POSIX systems, such like Linux, provide a faster but
non-reentrant implementation of synchronization primitives.</p>
<p><b>Read/write lock portability issues</b>: the <span class="lang">rwlock</span>
class is built on top of the POSIX rwlock interface, wherever available, or uses
the internal implementation (see <span class="lang">src/rwlock.cxx</span>). Various
system-level implementations use different prioritization schemes: they may be
'fair' with respect to both reader and writer threads, or a higher priority may
be given to one of them. Unfortunately the behaviour of rwlock is not standardized
yet. PTypes' internal implementation uses the 'fair' scheme which we believe is
the best and the only DoS-proof (denial-of-service) among other algorithms. On
the other hand, replacing the system-level rwlock with our own implementation
on all systems would lead to a preformance penalty compared to using 'native'
objects. We set this issue aside for some time and we are open to discuss it with
interested/experienced developers.</p>
<p class="seealso">See also: <a href="string.conversion.html">String Conversion</a>,
<a href="async.utils.html"></a><a href="streams.outstm.html">outstm</a>, <a href="streams.namedpipe.html">namedpipe</a>,
<a href="string.html">string</a>, <a href="async.utils.html">Multithreading Utilities</a></p>
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