ACE Software Development Guidelines

• General
  • Every text file must end with a newline.

  • Use spaces instead of tabs, except in Makefiles. Emacs users can add this to their .emacs:

    (setq-default indent-tabs-mode nil)

    Microsoft Visual C++ users should do the following:

            Choose:  Tools -- Options -- Tabs
            Then Set:  "Tab size" to 8 and "Indent size" to 2, and
            indent using spaces.
            

  • If you add a comment to code that is directed to, or requires the attention of, a particular individual: SEND EMAIL TO THAT INDIVIDUAL!.

  • Every program should have a ``usage'' message. It should be printed out if erroneous command line arguments, or a -? command line argument, are provided to the program.

  • The program main function should always be declared with arguments, e.g.,

            int
            main (int argc, char *argv[])
            {
              [...]
    
              return 0;
            }
            

    It should also return 0 on successful termination, and non-zero otherwise.

  • 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.

• Code Documentation
  • Use comments and whitespace (:-) liberally. Comments should consist of complete sentences, i.e., start with a captial letter and end with a period.

  • Insert a CVS/RCS keyword string at the top of every source file, Makefile, config file, etc. For C++ files, it is:

            // $Id$
            

    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.

    To insert that string at the top of a file:

            perl -pi -e \
              'if (! $o) {printf "// \$Id\$\n\n";}; $o = 1;' file
            

  • Comments, especially in header files, must follow the OSE Tools format requirements. Please see the ``Classinfo Tools'' section of the OSE ``Tools Manual'' for these requirements.

• Preprocessor
  • Never #include standard headers directly, except in a few specific ACE files, e.g., 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.

  • Always follow a preprocessor #endif with a /* */ C-style comment. It should correspond to the condition in the matching #if directive. For example,

            #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 */
            

  • Always insert a /**/ between an #include and filename, as shown in the above example. This avoids dependency problems with Visual C++.

  • Be very careful with names of macros and enum values. It's always best to prefix them with something like ACE_ or TAO_. There are too many system headers out there that #define OK, SUCCESS, ERROR, and so on.

  • Try to centralize #ifdefs with typedefs and #defines. For example, use this:

            #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 */
            

    instead of:

    
            #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 */
            

  • Protect header files against multiple inclusion with this construct:

            #ifndef FOO_H
            #define FOO_H
    
            [contents of header file]
    
            #endif /* FOO_H */
            

    This exact construct (note the #ifndef) 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.

    No code can appear after the final #endif for the optimization to be effective and correct.

• C++ Syntax and Constructs
  • for loops should look like:

            for (size_t i = 0; i < Options::instance ()->spawn_count (); ++i)
              spawn ();
            

    (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:)

            for (size_t i = 0; i < Options::instance ()->spawn_count (); ++i)
              {
                ACE_ASSERT (spawn () == 0);
              }
            

    Similarly, if statements should have a space after the ``if'', and no spaces just after the opening parenthesis and just before the closing parenthesis.

  • If a loop index is used after the body of the loop, it must be declared before the loop. For example,

            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';
            

  • Prefix operators are sometimes more efficient than postfix operators. Therefore, they are preferred over their postfix counterparts where the expression value is not used.

    Therefore, use this idiom for iterators, with prefix operator on the loop index:

           ACE_Ordered_MultiSet<int> set;
           ACE_Ordered_MultiSet_Iterator<int> iter(set);
    
           for (i = -10; i < 10; ++i)
             set.insert (2 * i + 1);
    
           

    rather than the postfix operator:

           for (i = -10; i < 10; i++)
             set.insert (2 * i + 1);
           

  • Avoid unnecessary parenthesis. We're not writing Lisp :-)

  • Put inline member functions in a .i file. That file is conditionally included by both the .h file, for example:

                class ACE_Export ACE_High_Res_Timer
                {
                  [...]
                };
    
                #if defined (__ACE_INLINE__)
                #include "ace/High_Res_Timer.i"
                #endif /* __ACE_INLINE__ */
                

    and .cpp file:

                #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)
                

    NOTE: 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 g++ with the -Wall option, will issue warnings for violations.

  • ACE_Export must be inserted between the class keyword and class name for all classes that are exported from libraries, as shown in the example above. However, do not use ACE_Export for template classes!

  • Mutators and accessors should be of this form:

            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.
            

    instead of the ``set_'' and ``get_'' form.

  • Never use delete to deallocate memory that was allocated with malloc. Similarly, never associate free with new. ACE_NEW or ACE_NEW_RETURN should be used to allocate memory, and delete should be used to deallocate it. And be careful to use the correct form, delete or delete [] to correspond to the allocation.

  • 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().

  • Always use ACE_NEW or ACE_NEW_RETURN to allocate memory, because they check for successful allocation and set errno appropriately if it fails.

  • Never compare or assign a pointer value with NULL; use 0 instead. The language allows any pointer to be compared or assigned with 0. The definition of NULL is implementation dependent, so it is difficult to use portably without casting.

  • Never cast a pointer to or from an int. On all currently supported ACE platforms, it is safe to cast a pointer to or from a long.

  • Be very careful when selecting an integer type that must be a certain size, e.g., 4 bytes. long 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.

  • If a class has any virtual functions, and its destructor is declared explicitly in the class, then the destructor should always 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 not be inline. (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.)

  • 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.

  • Initialization is usually cleaner than assignment, especially in a conditional. So, instead of writing code like this:

            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)
            

    Write it like this:

            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)
            

    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.

  • It is usually clearer to write conditionals that have both branches without a negated condition. For example,

            if (test)
              {
                // true branch
              }
            else
              {
                // false branch
              }
            

    is preferred over:

            if (! test)
              {
                // false test branch
              }
            else
              {
                // true test branch
              }
            

  • If a cast is necessary, avoid use of function-style casts, e.g., int (foo). Instead, use one of the ACE cast macros:

            return ACE_static_cast(size_t, this->count_) > that->size_;
            

    The general usage guidelines for the four styles of casts are:

    • ACE_const_cast: use to cast away constness, or volatile-ness.

    • ACE_static_cast: use to cast between compatible types, such as downcasting a pointer or narrowing an integer.

    • ACE_reinterpret_cast: use only when ACE_static_cast is not suitable.

    • ACE_dynamic_cast: avoid, unless you really want to type check at run-time.

  • 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:

            // Disallow copying by not implementing the following . . .
            ACE_Object_Manager (const ACE_Object_Manager &);
            ACE_Object_Manager &operator= (const ACE_Object_Manager &);
            

    If the class is a template class, then the ACE_UNIMPLEMENTED_FUNC macro should be used:

            // = Disallow copying...
            ACE_UNIMPLEMENTED_FUNC (ACE_TSS (const ACE_TSS<TYPE> &))
            ACE_UNIMPLEMENTED_FUNC (void operator= (const ACE_TSS<TYPE> &))
            

    ACE_UNIMPLEMENTED_FUNC can be used with non-template classes as well. Though for consistency and maximum safety, it should be avoided for non-template classes.

• I/O
  • Use ACE_DEBUG for printouts, and ACE_OS::scanf/fprintf () for file I/O. Avoid using iostreams because of implementation differences across platforms.

  • After attempting to open an existing file, always check for success. Take appropriate action if the open failed.

• UNICODE conformity
  • Define strings as ASYS_TCHAR if they need to be passed into system API. It expands to wchar_t only when ACE_HAS_MOSTLY_UNICODE_APIS is defined.

  • Use ASYS_TEXT and ASYS_WIDE_STRING for format strings and other string arguments passed to ACE_DEBUG or ACE_ERROR. For example,

              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));
              }
            

    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.

  • ACE_TRACE handles conversion between char strings and UNICODE strings automatically.

  • Other helper macros include ASYS_MULTIBYTE_STRING and ASYS_ONLY_MULTIBYTE_STRING. See the end of OS.h for more details.

• Exceptions
  • 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.

            #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;
            }
            

    Output is:

            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
    
            

ACE Usage Guidelines

• Always use ACE_OS (static) member functions instead of bare OS system calls.

• As a general rule, the only functions that should go into the ACE_OS class are ones that have direct equivalents on some OS platform. Functions that are extensions should go in the ACE class.

• Use the ACE_SYNCH_MUTEX macro, instead of using one of the specific mutexes, such as ACE_Thread_Mutex. This provides portability between threaded and non-threaded platforms.

• Avoid creating a static instance of user-defined (class) type. Instead, either create it as an ACE_Singleton, ACE_TSS_Singleton, or as an ACE_Cleanup object. See the ACE Singleton.h, Object_Manager.h, and Managed_Object.h header files for more information.

  Static instances of built-in types, such as int or any pointer type, are fine.

  Construction of static instance of a user-defined type should never 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.

• Do not use run-time type identification (RTTI). Some platforms do not support it.

• Do not use exception handling. Some platforms do not support it. And, it imposes an execution speed penalty.

• 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:

        ACE_NEW_RETURN (this->name_space_, LOCAL_NAME_SPACE, -1);
  
        if (ACE_LOG_MSG->op_status () != 0)
        ....
        

  This snip of code is from ACE_Naming_Context. All failed constructors in ACE (should) call ACE_ERROR. This sets the thread specific op_status, 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.

• Avoid using the C++ Standard Template Library (STL) in our applications. Some platforms do not support it yet.

Other ACE and TAO Guidelines

• Never add copyrighted, confidential, or otherwise restricted code to the ACE or TAO distributions without written permission from the owner.

CVS Usage Guidelines

• Always make sure that a change builds and executes correctly on at least one platform before checking it into the CVS repository.

Script Guidelines

• In general, it's best to write scripts in Perl.

• Follow the Perl style guide guide as closely as possible. man perlstyle to view it.
• 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 PATH:
  

        eval '(exit $?0)' && eval 'exec perl -S $0 ${1+"$@"}'
        & eval 'exec perl -S $0 $argv:q'
        if 0;
        

• If your Perl script relies on features only available in newer versions of Perl, include the a statement similar to the following:
  

          require 5.003;
        

• Don't depend on . 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 ..

Software Engineering Guidelines

• Advise: Keep other developers informed of problems and progress.

• Authorize: We have contractual obligations to not unilaterally change interfaces. If you need to change or remove an interface, get an OK.

• Minimize risk: Test all changes. Solicit review of changes.

• Revise only when necessary: Every change has risk, so avoid making any change unless there is a good reason for it.

• Normalize: Factor out commonality. For example, maintain a data value in only one place.

• Synthesize: 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.

ACE Design Rules

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