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<!-- $Id$ -->
<html>
<head>
<title>ACE Implementation Guidelines</title>
<link rev=made href="mailto:levine@cs.wustl.edu">
</head>
<body>
<center>
<h1>ACE Implementation Guidelines</h1>
<font size=-1>
Last modified <!--#echo var="LAST_MODIFIED" -->.<p>
</font>
</center>
<h2> </h2>
Thanks to Graham Dumpleton <grahamd@nms.otc.com.au> for providing
corrections to the OSE Classtools link and description. Thanks also
to Graham for providing the OSE tools!<p>
<h3>Coding Guidelines</h3>
<ul>
<li><strong>General</strong><p>
<ul>
<li>Every text file must end with a newline.<p>
<li>Use spaces instead of tabs, except in Makefiles. Emacs users
can add this to their <strong>.emacs</strong>:
<pre>(setq-default indent-tabs-mode nil)</pre></p>
Microsoft Visual C++ users should do the following:
<pre>
Choose: Tools -- Options -- Tabs
Then Set: "Tab size" to 8 and "Indent size" to 2, and
indent using spaces.
</pre><p>
<li>Every program should have a ``usage'' message. It should be
printed out if erroneous command line arguments, or a
<strong><code>-?</code></strong> command line argument, are
provided to the program.<p>
<li>The program <strong><code>main</code></strong> function should
always be declared with arguments, e.g.,
<pre>
int
main (int argc, char *argv[])
{
[...]
return 0;
}
</pre><p>
It should also return 0 on successful termination, and non-zero
otherwise.<p>
</ul>
<li><strong>Code Documentation</strong><p>
<ul>
<li>Use comments and whitespace (:-) liberally.<p>
<li>Insert a CVS/RCS keyword string at the top of every source file,
Makefile, config file, <em>etc</em>. For C++ files, it is:
<pre>
// $<!-- -->Id$
</pre>
It is not necessary to fill in the fields of the keyword string,
or modify them when you edit a file that already has one. CVS
does that automatically when you checkout or update the file.<p>
To insert that string at the top of a file:
<pre>
perl -pi -e 'if (! $o) {printf "// \$<!-- -->Id\$\n\n";}; $o = 1;' <em>file</em>
</pre><p>
<li>Comments, especially in header files, must follow the
<a href=http://www.dscpl.com.au>OSE</a> Tools format requirements.
Please see the ``Classinfo Tools'' section of the
<a href=http://www.dscpl.com.au>OSE</a> ``Tools Manual''
for these requirements.<p>
Please note that the Classinfo tools in OSE have been developed
independently since the copies in ACE were made and thus they
support new features not supported in the ACE version of the tools.
Certain subtle changes were also made in the ACE copies for
indicating sections, <em>etc.</em>, which makes them different
from the OSE documentation. Please see the
<a href=http://www.cs.wustl.edu/~schmidt/ACE-doctools.html>ACE-doctools
page</a> for descriptions of these changes.<p>
</ul>
<li><strong>Preprocessor</strong><p>
<ul>
<li>Never #include standard headers directly, except in a few
specific ACE files, <em>e.g.</em>, OS.h and stdcpp.h. Let
those files #include the correct headers. If you do not do
this, your code will not compile with the Standard C++ Library.<p>
<li>Always follow a preprocessor <strong><code>#endif</code></strong>
with a <strong><code>/* */</code></strong> C-style comment. It
should correspond to the condition in the matching
<strong><code>#if</code></strong> directive. For example,
<pre>
#if defined (ACE_HAS_THREADS)
# if defined (ACE_HAS_STHREADS)
# include /**/ <synch.h>
# include /**/ <thread.h>
# define ACE_SCOPE_PROCESS P_PID
# define ACE_SCOPE_LWP P_LWPID
# define ACE_SCOPE_THREAD (ACE_SCOPE_LWP + 1)
# else
# define ACE_SCOPE_PROCESS 0
# define ACE_SCOPE_LWP 1
# define ACE_SCOPE_THREAD 2
# endif /* ACE_HAS_STHREADS */
#endif /* ACE_HAS_THREADS */
</pre><p>
<li>Always insert a <strong><code>/**/</code></strong> between an
<strong><code>#include</code></strong> and
<strong><code>filename</code></strong>, as shown in the above
example. This avoids dependency problems with Visual C++.<p>
</ul>
<li><strong>C++ Syntax and Constructs</strong><p>
<ul>
<li><strong><code>for</code></strong> loops should look like:
<pre>
for (size_t i = 0; i < Options::instance ()->spawn_count (); i++)
spawn ();
</pre>
(though I prefer to always wrap the body of the loop in braces,
to avoid surprises when other code or debugging statements are
added, and to maintain sanity when the body consists of a macro,
such as ACE_ASSERT:)
<pre>
for (size_t i = 0; i < Options::instance ()->spawn_count (); i++)
{
ACE_ASSERT (spawn () == 0);
}
</pre><p>
Similarly, <strong><code>if</code></strong> statements should have
a space after the ``<strong>if</strong>'', and no spaces just after
the opening parenthesis and just before the closing parenthesis.<p>
<li>Avoid unnecessary parenthesis. We're not writing Lisp :-)<p>
<li>Put inline member functions in a <strong><code>.i</code></strong>
file. That file is conditionally included by both the
<strong><code>.h</code></strong> file, for example:<p>
<pre>
class ACE_Export ACE_High_Res_Timer
{
[...]
};
#if defined (__ACE_INLINE__)
#include "ace/High_Res_Timer.i"
#endif /* __ACE_INLINE__ */
</pre><p>
and <strong><code>.cpp</code></strong> file:<p>
<pre>
#define ACE_BUILD_DLL
#include "ace/High_Res_Timer.h"
#if !defined (__ACE_INLINE__)
#include "ace/High_Res_Timer.i"
#endif /* __ACE_INLINE__ */
ACE_ALLOC_HOOK_DEFINE(ACE_High_Res_Timer)
</pre><p>
<strong>NOTE:</strong> It is very important to ensure than an
inline function will not be used before its definition is seen.
Therefore, the inline functions in the .i file should be arranged
properly. Some compilers, such as <code>g++</code> with the
<code>-Wall</code> option, will issue warnings for violations.<p>
<li>Mutators and accessors should be of this form:<p>
<pre>
void object_addr (const ACE_INET_Addr &);
// Sets <object_addr_> cache from <host> and <port>.
ACE_INET_Addr &object_addr (void);
// Returns the <ACE_INET_Addr> for this profile.
</pre><p>
instead of the ``set_'' and ``get_'' form.<p>
<li>Never use <strong><code>delete</code></strong> to deallocate
memory that was allocated with <strong><code>malloc</code></strong>.
Similarly, never associate <strong><code>free</code></strong> with
<strong><code>new</code></strong>.
<strong><code>ACE_NEW</code></strong> or
<strong><code>ACE_NEW_RETURN</code></strong> should be used to
allocate memory, and <strong><code>delete</code></strong> should
be used to deallocate it. And be careful to use the correct form,
<strong><code>delete</code></strong> or
<strong><code>delete []</code></strong> to correspond to the
allocation.<p>
<li>Always use <strong><code>ACE_NEW</code></strong> or
<strong><code>ACE_NEW_RETURN</code></strong> to allocate memory,
because they check for successful allocation and set errno
appropriately if it fails.<p>
<li>Never compare or assign a pointer value with <strong>NULL</strong>;
use <strong>0</strong> instead. The language allows any pointer to
be compared or assigned with <strong>0</strong>. The definition
of <strong>NULL</strong> is implementation dependent, so it is
difficult to use portably without casting.<p>
<li>Never cast a pointer to or from an <strong><code>int</code></strong>.
On all currently supported ACE platforms, it is safe to cast
a pointer to or from a <strong><code>long</code></strong>.<p>
<li>Be very careful when selecting an integer type that must be a
certain size, <em>e.g.</em>, 4 bytes. <strong>long</strong> is
not 4 bytes on all platforms; it is 8 bytes on many 64-bit
machines. ACE_UINT32 is always 4 bytes, and ACE_UINT64 is
always 8 bytes.<p>
<li>If a class has any virtual functions, and its destructor is
declared explicitly in the class, then the destructor should
<strong>always</strong> be virtual as well. And to support
compiler activities such as generation of virtual tables and,
in some cases, template instantiation, the virtual destructor
should <strong>not be inline</strong>. (Actually, any non-pure
virtual function could be made non-inline for this purpose. But,
for convenience, if its performance is not critical, it is usually
easiest just to make the virtual destructor non-inline.)<p>
<li>Constructor initializers must appear in the same order as
the data members are declared in the class header. This avoids
subtle errors, because initialization takes place in the order
of member declaration.<p>
<li>Initialization is usually cleaner than assignment, especially
in a conditional. So, instead of writing code like this:
<pre>
ssize_t n_bytes;
// Send multicast of one byte, enough to wake up server.
if ((n_bytes = multicast.send ((char *) &reply_port, sizeof reply_port)) == -1)
</pre>
Write it like this:
<pre>
ssize_t n_bytes = multicast.send ((char *) &reply_port, sizeof reply_port)
// Send multicast of one byte, enough to wake up server.
if (n_bytes == -1)
</pre><p>
But, beware if the initialization is of a static variable.
A static variable is only initialized the first time its
declaration is seen. Of course, we should avoid using
static variables at all.<p>
<li>It is usually clearer to write conditionals that have
both branches without a negated condition. For example,<p>
<pre>
if (test)
{
// true branch
}
else
{
// false branch
}
</pre><p>
is preferred over:<p>
<pre>
if (! test)
{
// false test branch
}
else
{
// true test branch
}
</pre><p>
<li>If a cast is necessary, avoid use of ANSI-style casts,
<em>e.g.</em>, <code>int (foo)</code>. Instead, use
the ACE_static_cast macro:
<pre>
return ACE_static_cast(size_t, this->count_) > that->size_;
</pre><p>
<li>In general, if instances of a class should not be copied,
then a private copy constructor and assignment operator should
be declared for the class, but not implemented. For example:
<pre>
// Disallow copying by not implementing the following . . .
ACE_Object_Manager (const ACE_Object_Manager &);
ACE_Object_Manager &operator= (const ACE_Object_Manager &);
</pre><p>
If the class is a template class, then the
<code>ACE_UNIMPLEMENTED_FUNC</code> macro should be used:
<pre>
// = Disallow copying...
ACE_UNIMPLEMENTED_FUNC (ACE_TSS (const ACE_TSS<TYPE> &))
ACE_UNIMPLEMENTED_FUNC (void operator= (const ACE_TSS<TYPE> &))
</pre><p>
<code>ACE_UNIMPLEMENTED_FUNC</code> can be used with non-template
classes as well. Though for consistency and maximum safety, it
should be avoided for non-template classes.<p>
</ul>
<li><strong>I/O</strong><p>
<ul>
<li>Use <strong><code>ACE_DEBUG</code></strong> for printouts,
and <strong><code>ACE_OS::scanf/fprintf ()</code></strong> for
file I/O. Avoid using iostreams because of implementation
differences across platforms.<p>
</ul>
</ul><p>
<h3><a href="http://www.cs.wustl.edu/~schmidt/ACE-overview.html">ACE</a>
Usage Guidelines</h3>
<ul>
<li>Always use <strong><code>ACE_OS</code></strong> (static)
member functions instead of bare OS system calls.<p>
<li>Use the <strong><code>ACE_SYNCH_MUTEX</code></strong> macro,
instead of using one of the specific mutexes, such as
<strong><code>ACE_Thread_Mutex</code></strong>. This provides
portability between threaded and non-threaded platforms.<p>
<li>Avoid creating a static instance of user-defined (class) type.
Instead, either create it as an
<strong><code>ACE_Singleton</code></strong>,
<strong><code>ACE_TSS_Singleton</code></strong>, or as an
<strong><code>ACE_Cleanup</code></strong> object. See the
<strong>ACE</strong>
<a href="../ace/Singleton.h"><code>Singleton.h</code></a>,
<a href="../ace/Object_Manager.h"><code>Object_Manager.h</code></a>, and
<a href="../ace/Managed_Object.h"><code>Managed_Object.h</code></a>
header files for more information.<p>
Static instances of built-in types, such as
<strong><code>int</code></strong> or any pointer type, are fine.<p>
Construction of static instance of a user-defined type should
<em>never</em> spawn threads. Because order of construction of
statics across files is not defined by the language, it is usually
assumed that only one thread exists during static construction.
This allows statics suchs as locks to be safely created. We do not
want to violate this assumption.<p>
<li>Do not use run-time type identification (RTTI). Some platforms
do not support it.<p>
<li>Do not use exception handling. Some platforms do not support it.
And, it imposes an execution speed penalty.<p>
<li>Because ACE does not use exception handling, dealing with
failures requires a bit of care. This is especially true
in constructors. Consider the following approach:
<pre>
ACE_NEW_RETURN (this->name_space_, LOCAL_NAME_SPACE, -1);
if (ACE_LOG_MSG->op_status () != 0)
....
</pre>
This snip of code is from
<a href="../ace/Naming_Context.cpp"><code>ACE_Naming_Context</code></a>.
All failed constructors in ACE (should) call ACE_ERROR. This sets
the thread specific <strong>op_status</strong>, which can be checked
by the caller. This mechanism allows the caller to check for a failed
constructor without the requiring the constructor to throw
exceptions.<p>
<li>Avoid using the C++ Standard Template Library (STL) in our
applications. Some platforms do not support it yet.<p>
</ul><p>
<h3><a href="http://www.cs.wustl.edu/~schmidt/ACE-overview.html">ACE</a>
Design Rules</h3>
<dl>
<dt><strong>Initialization on first use is preferred over using static
initializations, especially when creating OO class
libraries.</strong> <em>I.e.</em>, use Double Check Locking.
<dd>This is a well known problem among OO C++ class designers. See
<em>Designing and Coding Reusable C++</em> by Caroll and Ellis,
for example.<p>
<dt>If you are parameterizing a searchable container template class
with readers/writer locks, do not use sentinels or any state
that requires updating during a a search.
<dd>....<p>
<dt>In multi-threaded objects, all methods should be re-entrant..<p>
<dt>Framework users should always use wrappers instead of directly
making system calls.
<dd>....<p>
<dt>Always guard against multiple inclusion of header files..<p>
<dt>Templates may require source. Hence, source files may need to
be guarded against multiple inclusion too.
<dt>Template classes should not be mixed with non-template classes..<p>
<dt>Guard against quirky compiler implementations through #define
abstractions (whereever possible)..<p>
<dt>Use consistent error-handling..<p>
<dt>Abstract away different representations of handles / file
descriptors..<p>
<dt>Avoid the use of global functions..<p>
<dt>If functions are required, place them within a namespace or
nested in a class..<p>
<dt>Avoid polluting the namespace..<p>
<dt>Don't use the inline keyword directly..<p>
<dt>Separate inline code into their own implementation files.
<em>I.e.</em> do not write code in header files..<p>
<dt>(Internationalization) Do not use the char type directly.
Abstract it for wide characters. Thus, do not assume your
character abstraction is a single byte..<p>
<dt>Don't use conditional compilation based on compiler/OS/hardware
platform, but upon available features..<p>
<dt>Centralize portability #ifdefs in a single place to ease
portability maintainence..<p>
<dt>Either check or return all return values (from framework
calls)..<p>
<dt>Apply strategy pattern to factor out common sources of variation
in a component..<p>
<dt>Use traits to merge multiple template arguments..<p>
<dt>Allow customization of memory allocation.<p>
<dt>Instrument framework methods to allow for run-time tracing.<p>
<dt>Avoid long chains of dereference operators.<p>
<dt>Use open() methods rather than constructors.
<p>
<dt>Instrument a dump() method in every object.
<p>
<dt>Qualify references to base class methods and data. <em>I.e.</em>,
anything outside the scope of the class.
<p>
<dt>Guard against multiple open() and close() calls, for
idempotency.
<p>
<dt>The state of an object does not need to be guarded in
destructors.
<p>
<dt>Base classes should not store information about derived
classes.
<p>
<dt>Don't make static objects whose correctness depends on
constructors being called. (That is, if 0 initialization is not
sufficient.)
<p>
<dt>Guarantee singleton destruction. <em>E.g.</em>, provide
hooks that allow singletons to be deleted before the process
exits.
<p>
<dt>All uses of the placement new operator must be accompanied by a
corresponding explicit destructor call.
<p>
<dt>In classes that require locking, have public methods acquire the
locks and call protected/private methods that do not acquire the
locks.
<p>
<dt>Try to minimize the number of template parameters passed to a
base class. Try to have a base class that is not a template,
from which specialized classes can be derived that may have
template parameters.
<p>
<dt>Define wrappers around clusters of functionality that are
semantically the same but may have accidental
incompatibilities. <em>E.g.</em>, semaphores, readers/writer
locks, mutex + condition variables, which can be used by
threads, processes, that may or may not reside on the same
machine.
<p>
<dt>Define generic components that can be parameterized by the
wrappers defined above (in the previous point).
<p>
<dt>Separate creation from use. <em>E.g.</em>, acceptor/connector and
service handler.
<p>
<dt>In searchable containers, separate traversal logic from item
operations.
<p>
<dt>...
</dl><p>
<h3><a href="http://www.cs.wustl.edu/~levine/CVS.html">CVS</a>
Usage Guidelines</h3>
<ul>
<li>Always make sure that a change builds and executes correctly
on at least one platform before checking it into the CVS repository.<p>
</ul><p>
<h3>Software Engineering Guidelines</h3>
<ul>
<li><strong>Advise</strong>: Keep other developers informed of problems
and progress.<p>
<li><strong>Authorize</strong>: We have contractual obligations to not
unilaterally change interfaces. If you need to change or remove an
interface, get an OK.<p>
<li><strong>Minimize</strong> risk: Test all changes. Solicit review of
changes.<p>
<li><strong>Revise</strong> only when necessary: Every change has risk,
so avoid making any change unless there is a good reason for it.<p>
<li><strong>Normalize</strong>: Factor out commonality. For example,
maintain a data value in only one place.<p>
<li><strong>Synthesize</strong>: Build stubs and scaffolding early to
simulate the complete system. Maintain a checked-in version of the
system that cleanly builds and tests at all times.<p>
</ul><p>
<hr>
<!-- hhmts start -->
Last modified: Fri Dec 5 17:29:17 CST 1997
<!-- hhmts end -->
</body>
</html>
|
