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<!-- $Id$ -->
<html>
<head>
<title>ACE Software Development Guidelines</title>
<link rev=made href="mailto:levine@cs.wustl.edu">
</head>
<BODY text = "#000000"
link="#000fff"
vlink="#ff0f0f"
bgcolor="#ffffff">
<hr>
<h3>ACE Software Development 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>If you add a comment to code that is directed to, or
requires the attention of, a particular individual:
<strong>SEND EMAIL TO THAT INDIVIDUAL!</strong>.<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>
<li>Avoid use of floating point types (float and double) and operations
unless absolutely necessary. Not all ACE platforms support them.
Therefore, wherever they are used, ACE_LACKS_FLOATING_POINT
conditional code must be also be used.<p>
</ul>
<li><strong>Code Documentation</strong><p>
<ul>
<li>Use comments and whitespace (:-) liberally. Comments
should consist of complete sentences, i.e., start
with a captial letter and end with a period.<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>
</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>
<li>Be very careful with names of macros and enum values. It's
always best to prefix them with something like <code>ACE_</code>
or <code>TAO_</code>. There are too many system headers out
there that #define <code>OK</code>, <code>SUCCESS</code>,
<code>ERROR</code>, and so on.<p>
<li>Try to centralize <code>#ifdefs</code> with <code>typedefs</code>
and <code>#defines</code>. For example, use this:
<pre>
#if defined(ACE_PSOS)
typedef long ACE_NETIF_TYPE;
# define ACE_DEFAULT_NETIF 0
#else /* ! ACE_PSOS */
typedef const ASYS_TCHAR* ACE_NETIF_TYPE;
# define ACE_DEFAULT_NETIF ASYS_TEXT("le0")
#endif /* ! ACE_PSOS */
</pre><p>
instead of:
<pre><p>
#if defined (ACE_PSOS)
// pSOS supports numbers, not names for network interfaces
long net_if,
#else /* ! ACE_PSOS */
const ASYS_TCHAR *net_if,
#endif /* ! ACE_PSOS */
</pre><p>
<li>Protect header files against multiple inclusion with this
construct:
<pre>
#ifndef FOO_H
#define FOO_H
[contents of header file]
#endif /* FOO_H */
</pre><p>
This exact construct (note the <code>#ifndef</code>)
is optimized by many compilers such they only open the
file once per compilation unit. Thanks to Eric C. Newton
<ecn@smart.net> for pointing that out.<p>
If the header <code>#includes</code> an ACE library header,
then it's a good idea to include the <code>#pragma once</code>
directive:
<pre>
#ifndef FOO_H
#define FOO_H
#include "ace/ACE.h"
#if !defined (ACE_LACKS_PRAGMA_ONCE)
# pragma once
#endif /* ACE_LACKS_PRAGMA_ONCE */
[contents of header file]
#endif /* FOO_H */
</pre><p>
<code>#pragma once</code> must be protected, because some
compilers complain about it. The protection depends on
<code>ACE_LACKS_PRAGMA_ONCE</code>, which is defined in
some ACE config headers. Therefore, the protected
<code>#pragma once</code> construct should only be used after
an <code>#include</code> of an ACE library header. Note that
many compilers enable the optimization if the <code>#ifndef</code>
protection construct is used, so for them, <code>#pragm once</code>
is superflous.<p>
<strong>No</strong> code can appear after the final
<code>#endif</code> for the optimization to be effective and
correct.<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>If a loop index is used after the body of the loop, it
<strong>must</strong> be declared before the loop. For example,
<pre>
size_t i = 0;
for (size_t j = 0; file_name [j] != '\0'; ++i, ++j)
{
if (file_name [j] == '\\' && file_name [j + 1] == '\\')
++j;
file_name [i] = file_name [j];
}
// Terminate this string.
file_name [i] = '\0';
</pre><p>
<li>Prefix operators are sometimes more efficient than postfix
operators. Therefore, they are preferred over their postfix
counterparts where the expression value is not used.<p>
Therefore, use this idiom for iterators, with prefix operator
on the loop index:
<pre>
ACE_Ordered_MultiSet<int> set;
ACE_Ordered_MultiSet_Iterator<int> iter(set);
for (i = -10; i < 10; ++i)
set.insert (2 * i + 1);
</pre>
rather than the postfix operator:
<pre>
for (i = -10; i < 10; i++)
set.insert (2 * i + 1);
</pre><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><code>ACE_Export</code> must be inserted between the
<code>class</code> keyword and class name for all classes that
are exported from libraries, as shown in the example above.
<strong>However</strong>, do <strong>not</strong> use
<code>ACE_Export</code> for template classes!<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>Don't check for a pointer being 0 before deleting it. It's
always safe to delete a 0 pointer. If the pointer is visible
outside the local scope, it's often a good idea to 0 it
_after_ deleting it. Note, the same argument applies to
free().<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 function-style casts,
<em>e.g.</em>, <code>int (foo)</code>. Instead, use
one of the ACE cast macros:
<pre>
return ACE_static_cast(size_t, this->count_) > that->size_;
</pre><p>
The general usage guidelines for the four styles of casts are:<p>
<ul>
<li><strong>ACE_const_cast</strong>: use to cast away
constness, or volatile-ness.<p>
<li><strong>ACE_static_cast</strong>: use to cast between
compatible types, such as downcasting a pointer or narrowing
an integer.<p>
<li><strong>ACE_reinterpret_cast</strong>: use only when
ACE_static_cast is not suitable.<p>
<li><strong>ACE_dynamic_cast</strong>: avoid, unless you really
want to type check at run-time.<p>
</ul>
<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>
<li>After attempting to open an existing file, always check for success.
Take appropriate action if the open failed.<p>
</ul>
<li><strong>UNICODE conformity</strong><p>
<ul>
<li>Define strings as <strong><code>ASYS_TCHAR</code></strong> if
they need to be passed into system API. It expands to
<code>wchar_t</code> only when
<code>ACE_HAS_MOSTLY_UNICODE_APIS</code> is defined.<p>
<li>Use <strong><code>ASYS_TEXT</code></strong> and
<strong><code>ASYS_WIDE_STRING</code></strong> for format
strings and other string arguments passed to
<code>ACE_DEBUG</code> or <code>ACE_ERROR</code>. For
example,<p>
<pre>
void
ACE_FOO::ace_bar (int err, ASYS_TCHAR *astr)
{
ACE_TRACE ("ACE_FOO::ace_bar");
ACE_DEBUG ((LM_DEBUG, ASYS_TEXT ("From ACE_FOO::ace_bar")));
if (err)
ACE_ERROR ((LM_ERROR,
ASYS_TEXT ("(%P) Printing this string %s\n"),
astr));
}
</pre>
<p>
This is because ACE also support platforms which use UNICODE
in most of their APIs. On these platforms, ACE also uses
UNICODE as its system string type.<p>
<li><strong><code>ACE_TRACE</code></strong> handles conversion
between char strings and UNICODE strings automatically.<p>
<li>Other helper macros include
<strong><code>ASYS_MULTIBYTE_STRING</code></strong> and
<strong><code>ASYS_ONLY_MULTIBYTE_STRING</code></strong>. See
the end of <a href="../ace/OS.h">OS.h</a> for more details.<p>
</ul><p>
<li><strong>Exceptions</strong><p>
<ul>
<li>There are many ways of throwing and catching exceptions. The
code below gives several examples. Note that each method has
different semantics and costs. Whenever possible, use the
first approach.<p>
<pre>
#include "iostream.h"
class exe_foo
{
public:
exe_foo (int data) : data_ (data)
{ cerr << "constructor of exception called" << endl; }
~exe_foo ()
{ cerr << "destructor of exception called" << endl; }
exe_foo (const exe_foo& foo) : data_ (foo.data_)
{ cerr << "copy constructor of exception called" << endl; }
int data_;
};
void
good (int a)
{
throw exe_foo (a);
};
void
bad (int a)
{
exe_foo foo (a);
throw foo;
};
int main ()
{
cout << endl << "First exception" << endl << endl;
try
{
good (0);
}
catch (exe_foo &foo)
{
cerr << "exception caught: " << foo.data_ << endl;
}
cout << endl << "Second exception" << endl << endl;
try
{
good (0);
}
catch (exe_foo foo)
{
cerr << "exception caught: " << foo.data_ << endl;
}
cout << endl << "Third exception" << endl << endl;
try
{
bad (1);
}
catch (exe_foo &foo)
{
cerr << "exception caught: " << foo.data_ << endl;
}
cout << endl << "Fourth exception" << endl << endl;
try
{
bad (1);
}
catch (exe_foo foo)
{
cerr << "exception caught: " << foo.data_ << endl;
}
return 0;
}
</pre>
Output is: <p>
<pre>
First exception
constructor of exception called
exception caught: 0
destructor of exception called
Second exception
constructor of exception called
copy constructor of exception called
exception caught: 0
destructor of exception called
destructor of exception called
Third exception
constructor of exception called
copy constructor of exception called
destructor of exception called
exception caught: 1
destructor of exception called
Fourth exception
constructor of exception called
copy constructor of exception called
destructor of exception called
copy constructor of exception called
exception caught: 1
destructor of exception called
destructor of exception called
</pre>
</ul><p>
</ul>
<hr>
<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>As a general rule, the only functions that should go into the
<strong><code>ACE_OS</code></strong> class are ones that have
direct equivalents on some OS platform. Functions that are
extensions should go in the <strong><code>ACE</code></strong> class.<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>
<hr>
<h3><a href="http://www.cs.wustl.edu/~schmidt/ACE-overview.html">Other
ACE</a> and
<a href="http://www.cs.wustl.edu/~schmidt/TAO-overview.html">TAO</a>
Guidelines</h3>
<ul>
<li>Never add copyrighted, confidential, or otherwise restricted
code to the ACE or TAO distributions without written permission
from the owner.<p>
</ul>
<hr>
<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>
<hr>
<h3>Script Guidelines</h3>
<ul>
<li>In general, it's best to write scripts in Perl.<p>
<li>Follow the Perl style guide guide as closely as
possible. <code>man perlstyle</code> to view it.
<li>Don't specify a hard-coded path to Perl itself. Use
the following code at the top of the script to pick up
perl from the users <code>PATH</code>:<br>
<pre>
eval '(exit $?0)' && eval 'exec perl -S $0 ${1+"$@"}'
& eval 'exec perl -S $0 $argv:q'
if 0;
</pre><p>
<li>If your Perl script relies on features only available
in newer versions of Perl, include the a statement similar
to the following:<br>
<pre>
require 5.003;
</pre>
<li>Don't depend on <strong><code>.</code></strong> being
in the user's path. If the script spawns another executable
that is supposed to be in the current directory, be sure the
prefix its filename with <strong><code>.</code></strong>.<p>
</ul>
<hr>
<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>
<hr>
<h3><a href="http://www.cs.wustl.edu/~schmidt/rules.html">ACE
Design Rules</a></h3>
<hr> <P>
<font size=-1>
Last modified <!--#echo var="LAST_MODIFIED" -->.<p>
</font>
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