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.
        
```
- Do not end text lines with spaces. Emacs users can add this to their .emacs:
```
(setq-default nuke-trailing-whitespace-p t)
```
  Note for Microsoft Visual Studio .NET Users:
  There is a macro project (ace_guidelines.vsmacros) located in $ACE_ROOT/docs that replaces tabs with spaces and removes trailing spaces each time you save a file.
- Try to limit the length of source code lines to less than 80 characters. Users with 14 inch monitors appreciate it when reading code. And, it avoids mangling problems with email and net news.
- Try to avoid creating files with excessively long names (45 characters). Moreover, ensure that the names of generated files e.g. MakeProjectCreator, tao_idl do not also go beyond that limit. Some operating systems cannot handle very long file names correctly.
- 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.
- An ACE-using program's entry point should use the portable form:
```
        int ACE_TMAIN (int argc, ACE_TCHAR *argv[])
        
```
  This form is portable to all ACE platforms whether using narrow or wide characters. The other two common forms:
```
        int main (int argc, char *argv[])
        int wmain (int argc, wchar_t *argv[])
        
```
  as well as any other main entrypoint form should only be used when there is some overarching reason to not use the portable form. One example would be a Windows GUI program that requires WinMain.
  See $ACE_ROOT/docs/wchar.txt for more information on ACE support on wchar.
- The program entry point function, in any form mentioned above, must always be declared with arguments, e.g.,
```
        int
        ACE_TMAIN (int argc, ACE_TCHAR *argv[])
        {
          [...]

          return 0;
        }
        
```
  If you don't use the argc and/or argv arguments, don't declare them, e.g.,
```
        int
        ACE_TMAIN (int, ACE_TCHAR *[])
        {
          [...]

          return 0;
        }
        
```
  Please declare the second argument as ACE_TCHAR *[] instead of ACE_TCHAR ** or char *[]. Ancient versions of MSC++ complained about ACE_TCHAR ** and char *[] is not Unicode-compliant.
  main must 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.
- Avoid including the string "Error" in a source code filename. GNU Make's error messages start with "Error". So, it's much easier to search for errors if filenames don't contain "Error".
- Narrow interfaces are better than wide interfaces. If there isn't a need for an interface, leave it out. This eases maintenance, minimizes footprint, and reduces the likelihood of interference when other interfaces need to be added later. (See the ACE_Time_Value example .
- Never use assert() macros or related constructs (such as abort()) calls in core ACE, TAO, and CIAO library/framework code. These macros are a major problem for production software that uses this code since the error-handling strategy (i.e., abort the process) is excessive. Instead, extract out the expressions from assert() macros and use them as precondition/postconditions/invariants in the software and return any violations of these conditions/invariants via exceptions or error return values. It's fine to use assert() macros et al. in test programs, but make sure these tests never find their way into the core ACE, TAO, and CIAO library/framework code base.

Coding Style

When writing ACE, TAO, and CIAO class and method names make sure to use underscores ('_') to separate the parts of a name rather than intercaps. For example, use

        class ACE_Monitor_Control
        {
        public:
          int read_monitor (void);
          // ...
        };

rather than

        class ACEMonitorControl
        {
        public:
          int readMonitor (void);
          // ...
        };

Code Documentation
- Use comments and whitespace (:-) liberally. Comments should consist of complete sentences, i.e., start with a capital letter and end with a period.
- Insert a svn 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. SVN 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
        
```
- Be sure to follow the guidelines and restrictions for use of the documentation tools for ACE header files, which must follow the Doxygen format requirements. The complete documentation for Doxygen is available in the Doxygen manual. For an example header file using Doxygen-style comments, please refer to ACE.h.
- The header file comment should at least contain the following entries:
```
        /**
         * @file Foo.h
         * @author Authors Name <[email protected]>
         *
         *  A few words describing the file.
         */
        
```
- A class should be commented this way:
```
        /**
         * @class Foo_Impl
         * @brief A brief description of the class
         *
         * A more detailed description.
         */
        
```
- The preferred way to document methods is:
```
         /// This function foos the bars
         /// another line of documentation if necessary
         /// @param bar The bar you want to foo
         void foo (int bar);
         
```
- All binary options for ACE and TAO should be specified in terms of the integral values 0 and 1, rather than "true" and "false" or "yes" and "no". All TAO options should be documented in the online TAO options document.
  .
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 use #if defined (MACRONAME) to test if a macro is defined, rather than the simpler #if MACRONAME. Doxygen requires this. The one exception to this the macros used to prevent multiple inclusion of header files, as shown below.
- Always follow a preprocessor #endif with a /* */ C-style comment. Using C-style comments with preprocessor code is required for some old compilers. 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 */
        
```
- Be sure to put spaces around comment delimiters, e.g., char * /* foo */ instead of char */*foo*/. MS VC++ complains otherwise.
- Always insert a /**/ between an #include and filename, for system headers and ace/pre.h and ace/post.h as shown in the above example. This avoids dependency problems with Visual C++ and prevents Doxygen from including the headers in the file reference trees.
- Be very careful with names of macros, enum values, and variables 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, index, s_type, and so on.
- When using macros in an arithmetic expression, be sure to test that the macro is defined, using defined(macro) before specifying the expression. For example:
```
#if __FreeBSD__ < 3
```
  will evaluate true on any platform where __FreeBSD__ is not defined. The correct way to write that guard is:
```
#if defined (__FreeBSD__)  &&  __FreeBSD__ < 3
```
  If using g++, problems like this can be flagged as a warning by using the "-Wundef" command line option.
- 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 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 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 <[email protected]> for pointing that out.
  If the header #includes an ACE library header, then it's a good idea to include the #pragma once directive:
```
        #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 */
        
```
  #pragma once must be protected, because some compilers complain about it. The protection depends on ACE_LACKS_PRAGMA_ONCE, which is defined in some ACE config headers. Therefore, the protected #pragma once construct should only be used after an #include of an ACE library header. Note that many compilers enable the optimization if the #ifndef protection construct is used, so for them, #pragma once is superfluous.
  No code can appear after the final #endif for the optimization to be effective and correct.
- Files that contain parametric classes should follow this style:
```
      #ifndef FOO_T_H
      #define FOO_T_H

      #include "ace/ACE.h"
      #if !defined (ACE_LACKS_PRAGMA_ONCE)
      # pragma once
      #endif /* ACE_LACKS_PRAGMA_ONCE */

      // Put your template declarations here...

      #if defined (__ACE_INLINE__)
      #include "Foo_T.inl"
      #endif /* __ACE_INLINE__ */

      #if defined (ACE_TEMPLATES_REQUIRE_SOURCE)
      #include "Foo_T.cpp"
      #endif /* ACE_TEMPLATES_REQUIRE_SOURCE */

      #if defined (ACE_TEMPLATES_REQUIRE_PRAGMA)
      #pragma implementation "Foo_T.cpp"
      #endif /* ACE_TEMPLATES_REQUIRE_PRAGMA */

      #endif /* FOO_T_H */
```
  Notice that some compilers need to see the code of the template, hence the .cpp file must be included from the header file.
  
  To avoid multiple inclusions of the .cpp file it should also be protected as in:
```
      #ifndef FOO_T_CPP
      #define FOO_T_CPP

      #include "Foo_T.h"
      #if !defined (ACE_LACKS_PRAGMA_ONCE)
      # pragma once
      #endif /* ACE_LACKS_PRAGMA_ONCE */

      #if !defined (__ACE_INLINE__)
      #include "ace/Foo_T.inl"
      #endif /* __ACE_INLINE__ */

      // put your template code here

      #endif /* FOO_T_H */
```
  Finally, you may want to include the template header file from a non-template header file (check $ACE_ROOT/ace/Synch.h); in such a case the template header should be included after the inline function definitions, as in:
```
      #ifndef FOO_H
      #define FOO_H

      #include "ace/ACE.h"
      #if !defined (ACE_LACKS_PRAGMA_ONCE)
      # pragma once
      #endif /* ACE_LACKS_PRAGMA_ONCE */

      // Put your non-template declarations here...

      #if defined (__ACE_INLINE__)
      #include "Foo.inl"
      #endif /* __ACE_INLINE__ */

      #include "Foo_T.h"

      #endif /* FOO_H */
```
- Avoid #include <math.h> if at all possible. The /usr/include/math.h on SunOS 5.5.1 through 5.7 defines a struct name exception, which complicates use of exceptions.
- On a .cpp file always include the corresponding header file first, like this:
```
        // This is Foo.cpp

        #include "Foo.h"
        #include "tao/Bar.h"
        #include "ace/Baz.h"

        // Here comes the Foo.cpp code....
```
  In this way we are sure that the header file is self-contained and can be safely included from some place else.
- In the TAO library never include <corba.h>, this file should only be included by the user and introduces cyclic dependencies in the library that we must avoid.
- Never include a header file when a forward reference will do, remember that templates can be forward referenced too. Consult your favorite C++ book to find out when you must include the full class definition.
C++ Syntax and Constructs
- for loops should look like:
```
        for (unsigned int i = 0; i < count; ++i)
          ++total;
        
```
  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 an ACE_ASSERT without a trailing semicolon:
```
        for (unsigned int i = 0; i < count; ++i)
          {
            ACE_ASSERT (++total < UINT_MAX;)
          }
        
```
  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 generally 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);
       
```
- Prefer using if (...) else .... instead of ?: operator. It is a lot less error prone, and will help you avoid bugs caused due to the precedence of ?: , compared with other operators in an expression.
- When a class provides operator==, it must also provide operator!=. Also, both these operators must be const and return bool.
- Avoid unnecessary parenthesis. We're not writing Lisp :-)
- Put inline member functions in a .inl 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.inl"
            #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.inl"
            #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 .inl file should be arranged properly. Some compilers, such as g++ with the -Wall option, will issue warnings for violations.
- Some inlining heuristics:
  - One liners should almost always be inline, as in:
```
ACE_INLINE
Foo::bar ()
{
  this->baz ();
}
```
  - The notable exception is virtual functions, which should generally not be inlined.
  - Big (more than 10 lines) and complex function (more than one if () statement, or a switch, or a loop) should not be inlined.
  - Medium sized stuff depends on how performance critical it is. If you know that it's in the critical path, then make it inline. When in doubt, profile the code.
- 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 or classes that are not used out of the ACE library, for example.!
- Mutators and accessors should be of this form:
```
        /// Sets @c object_addr_ cache from @c host and @c port.
        void object_addr (const ACE_INET_Addr &);

        /// Returns the ACE_INET_Addr for this profile.
        const ACE_INET_Addr &object_addr const (void);
        
```
  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 or a long. On all currently supported ACE platforms, it is safe to cast a pointer to or from intptr_t or uintptr_t (include ace/Basic_Types.h).
- 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.)
- Avoid default arguments unless there's a good reason. For an example of how they got us into a jam is:
```
        ACE_Time_Value (long sec, long usec = 0);
        
```
  So, ACE_Time_Value (2.5) has the unfortunate effect of coercing the 2.5 to a long with value 2. That's probably not what the programmer intended, and many compilers don't warn about it.
  A nice fix would be to add an ACE_Time_Value (double) constructor. But, that would cause ambiguous overloading due to the default value for the second argument of ACE_Time_Value (long sec, long usec = 0). We're stuck with ACE_Time_Value, but now we know that it's easy to avoid.
- 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 (and non-constant) 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 C-style "sledgehammer" casts. Use standard C++ casts (e.g. static_cast<int> (foo)) instead.
- 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.
- Never use BOOL, or similar types. (ACE_CDR::Boolean and CORBA::Boolean are acceptable). Use the standard C++ bool for boolean variables, instead.
- Functions should always return -1 to indicate failure, and 0 or greater to indicate success.
- Separate the code of your templates from the code for non-parametric classes: some compilers get confused when template and non-template code is mixed in the same file.
- It's a good idea to specify the include path (with -I) to include any directory which contains files with template definitions. The Compaq Tru64 cxx -ptv compiler option may help diagnose missing template instantiation problems.
- When referring to member variables and functions, use this->member. This makes it clear to the reader that a class member is being used. It also makes it crystal clear to the compiler which variable/function you mean in cases where it might make a difference.
- Don't use template template arguments, this C++ construct is not supported by the HP aCC 3.70 compiler at this moment. For example the following template decleration is one that just doesn't work.
```
        template<typename S_var, size_t BOUND, template <typename> class Insert_Policy> class A {};
        
```
I/O
- Use ACE_DEBUG for printouts, and ACE_OS::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.
- Notice that ACE_DEBUG and ACE_ERROR don't support %ld of any other multicharacter format.
WCHAR conformity
- For ACE, use ACE_TCHAR instead of char for strings and ACE_TEXT() around string literals. Exceptions are char arrays used for data and strings that need to remain as 1 byte characters.
- If you have a char string that needs to be converted to ACE_TCHAR, use the ACE_TEXT_CHAR_TO_TCHAR() macro. If you have a ACE_TCHAR string that needs to be converted to a char string, use the ACE_TEXT_ALWAYS_CHAR() macro
- Do not use the Win32 TCHAR macros. The wide character-ness of ACE is separate from UNICODE and _UNICODE.
- For TAO, don't use ACE_TCHAR or ACE_TEXT. The CORBA specification defines APIs as using char. So most of the time there is no need to use wide characters.

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

Compilation
- Whenever you add a new test or example to ACE or TAO, make sure that you modify the MPC file in the parent directory. This will make sure that your code gets compiled on a regular basis.

ACE Shared Libary Guidelines

Create a separate export macro for each dynamic library. A header file containing the export macro and additional support macros should be generated by using the ACE_wrappers/bin/generate_export_file.pl Perl script.
Make sure that your classes, structures and free functions are annotated with this export macro. The only exceptions are pure template classes, structures and free functions.

Only classes (and structures, free functions, etc) that are part of the library public interface must be exported (e.g. declared with an export macro). Those that are only meant to be used internally need not be exported, particularly for g++ >=4.0 since doing so defeats some neat optimizations. Here's a common case in where an export macro is generally used unnecessarily:
```
class FooExport Foo
{
public:
  virtual void kung_fu () = 0;
};

class FooExport Bar : public Foo
{
public:
  virtual void kung_fu ()  { ... }
};

class FooExport FooFactory
{
public:
  Foo * make_foo ()
    {
      // Assume that this implementation is hidden from
      // the application and is consequently out of line.
      return new Bar();
    }
};
          
```
Here the application is only meant to invoke operations through a pointer or reference to the abstract base class "Foo" created by the "FooFactory", not the "Bar" subclass. In this case, exporting "Bar" is unnecessary. If your concrete class is meant to be used outside of the shared library (e.g. as a template parameter, within a dynamic_cast<>, etc) you must then export it. Otherwise, avoid doing so if you can.
Make sure that you specify that you are creating a dynamic library in your MPC file by adding a sharedname tag.
Make sure that you add the FOO_BUILD_DLL preprocessor symbol to the dynamicflags of the MPC project that is used to build a library. Note that the export files are setup such that when this macro is defined, the symbols are exported, otherwise they are imported. The default behaviour is to set up for import so that clients of your library don't need to worry about arcane build flags like FOO_BUILD_DLL in their build setup. This ties back to the first item.
When you specify the order of libraries to link to, make sure that the dependent libraries come after the libraries which depend on them, i.e., your link line should always contain -lDependsOnFoo -lFoo. Note that this is not a requirement on GNU/Linux but linkers on other platforms are not as forgiving.
Use the ACE_SINGLETON_DECLARE macro to declare a class as a singleton. Declare exported (i.e. default visibility) singleton templates prior to typedefs that reference them. This prevents g++ 4.0 from silently making their visibility hidden (see Bug 2260 for details).
Avoid inlining virtual functions in classes that must be exported since doing so can cause RTTI related problems (e.g. dynamic_cast<> failures) when using g++ >= 4.0 due to our use of that compiler's "visibility attribute" support that is tied in to the export macros. This includes virtual destructors automatically created by the compiler when you don't declare one. Make sure you define a no-op out-of-line virtual destructor if your base class has a virtual destructor since you may otherwise run into the mentioned RTTI problems.

ACE Usage Guidelines

Always use the ACE_OS namespace functions instead of bare OS system calls.
As a general rule, the only functions that should go into the ACE_OS namespace are ones that have direct equivalents on some OS platform. Functions that are extensions should go in the ACE namespace.
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 C++ exception handling directly. Some platforms do not support it. And, it can impose an execution speed penalty. Instead use the TAO/ACE try/catch macros.
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.
Another consequence of ACE's avoidance of exception handling is that you should use open() methods on classes that perform initializations that can fail. This is because open() returns an error code that's easily checked by the caller, rather than relying on constructor and thread-specific status values.
Avoid using the C++ Standard Template Library (STL) in our applications. Some platforms do not support it yet. It is safe to use the STL generic algoritms. The following have been used already and don't seem to cause any portability issues:
```
	std::swap
	std::for_each
	std::fill
	std::generate
	std::transform
	std::copy
      
```
Be very careful with ACE_ASSERT. It must only be used to check values; it may never be used to wrap a function call, or contain any other side effect. That's because the statement will disappear when ACE_NDEBUG is enabled. For example, this code is BAD:
```
      ACE_ASSERT (this->next (retv) != 0);  // BAD CODE!
      
```
Instead, the above should be coded this way:
```
      int const result = this->next (retv);
      ACE_ASSERT (result != 0);
      ACE_UNUSED_ARG (result);
      
```
Never put side effects in ACE_DEBUG code:
```
      ACE_DEBUG ((LM_DEBUG,
                 "handling signal: %d iterations left\n",
                 --this->iterations_));        // BAD CODE!
      
```
Note that this won't work correctly if ACE_NDEBUG is defined, for the same reason that having side-effects in ACE_ASSERTs won't work either, i.e., because the code is removed.
Be very careful with the code that you put in a signal handler. On Solaris, the man pages document systems calls as being Async-Signal-Safe if they can be called from signal handlers. In general, it's best to just set a flag in a signal handler and take appropriate action elsewhere. It's also best to avoid using signals, especially asynchronous signals.
Immediately after opening a temporary file, unlink it. For example:
```
      ACE_HANDLE h = open the file (filename);

      ACE_OS::unlink (filename);
      
```
This avoids leaving the temporary file even if the program crashes.
Be sure to specify the THR_BOUND thread creation flag for time-critical threads. This ensures that the thread competes for resources globally on Solaris. It is harmless on other platforms.

Other ACE and TAO Guidelines

When enhancing, updating, or fixing ACE or TAO, always:
1. Test your change on at least Windows and Linux before commiting. After commiting watch the scoreboard to catch errors your change may be related to on other platforms.
2. An an entry to the appropriate ChangeLog. TAO and some ACE subdirectories, such as ASNMP, JAWS, and gperf, have their own ChangeLogs. If you don't use one of those, use the ChangeLog in the top-level ACE_wrappers directory. A ChangeLog entry should have the form:
```
<tab> * dir/file.ext [(methods)]: description...
```
  If you have a number of files, the names should be on separate lines. In this case, it's also ok to start the description on a new line indented to "dir."
3. Commit your change using a message of this form:
  ChangeLogTag: Thu Jul 22 09:55:10 UTC 1999 David L. Levine <[email protected]>
4. If the change is in response to a request by someone else:
  1. Make sure that person is acknowledged in ACE_wrappers/THANKS, and
  2. Respond to that person.
Never add copyrighted, confidential, or otherwise restricted code to the ACE or TAO distributions without reviewing the situation with DOC management (i.e. Doug Schmidt). You will also most likely need to get written permission from the owner. The particular language and form needed will be relayed to you after discussing it with DOC management.

SVN Usage Guidelines

Always make sure that a change builds and executes correctly on at least one platform before checking it into the SVN repository. All changes must be tested with g++ before commiting. That means you may need to test on at least two platforms.

Script Guidelines

In general, it's best to write scripts in Perl. It's OK to use Bourne shell. Never, never, never use csh, ksh, bash, or any other kind of shell.
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;
      
```
Never, never, never start the first line of a script with "#", unless the first line is "#! /bin/sh". With just "#", t/csh users will spawn a new shell. That will cause their .[t]cshrc to be processed, possibly clobbering a necessary part of their environment.
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.
Be available: Breaking compilation in one platform or another should be avoided (see above), but it is bound to happen when so many platforms are in use. Be available after making a change, if you won't be available for at least 48 hours after the change is made then don't make it!

ACE Design Rules

Last modified: Wed Nov 23 11:00:44 CST 2005

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