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diff --git a/rubbos/app/httpd-2.0.64/srclib/apr/docs/APRDesign.html b/rubbos/app/httpd-2.0.64/srclib/apr/docs/APRDesign.html deleted file mode 100644 index 7d1caeb8..00000000 --- a/rubbos/app/httpd-2.0.64/srclib/apr/docs/APRDesign.html +++ /dev/null @@ -1,399 +0,0 @@ -<HTML> -<HEAD><TITLE>APR Design Document</TITLE></HEAD> -<BODY> -<h1>Design of APR</h1> - -<p>The Apache Portable Run-time libraries have been designed to provide a common -interface to low level routines across any platform. The original goal of APR -was to combine all code in Apache to one common code base. This is not the -correct approach however, so the goal of APR has changed. There are places -where common code is not a good thing. For example, how to map requests -to either threads or processes should be platform specific. APR's place -is now to combine any code that can be safely combined without sacrificing -performance.</p> - -<p>To this end we have created a set of operations that are required for cross -platform development. There may be other types that are desired and those -will be implemented in the future.</p> - -<p>This document will discuss the structure of APR, and how best to contribute -code to the effort.</p> - -<h2>APR On Windows and Netware</h2> - -<p>APR on Windows and Netware is different from APR on all other systems, -because those platforms don't use autoconf. On Unix, apr_private.h (private to -APR) and apr.h (public, used by applications that use APR) are generated by -autoconf from acconfig.h and apr.h.in respectively. On Windows (and Netware), -apr_private.h and apr.h are created from apr_private.hw (apr_private.hwn) -and apr.hw (apr.hwn) respectively.</p> - -<p> <strong> - If you add code to acconfig.h or tests to configure.in or aclocal.m4, - please give some thought to whether or not Windows and Netware need - these additions as well. A general rule of thumb, is that if it is - a feature macro, such as APR_HAS_THREADS, Windows and Netware need it. - In other words, if the definition is going to be used in a public APR - header file, such as apr_general.h, Windows needs it. - - The only time it is safe to add a macro or test without also adding - the macro to apr*.h[n]w, is if the macro tells APR how to build. For - example, a test for a header file does not need to be added to Windows. -</strong></p> - -<h2>APR Features</h2> - -<p>One of the goals of APR is to provide a common set of features across all -platforms. This is an admirable goal, it is also not realistic. We cannot -expect to be able to implement ALL features on ALL platforms. So we are -going to do the next best thing. Provide a common interface to ALL APR -features on MOST platforms.</p> - -<p>APR developers should create FEATURE MACROS for any feature that is not -available on ALL platforms. This should be a simple definition which has -the form:</p> - -<code>APR_HAS_FEATURE</code> - -<p>This macro should evaluate to true if APR has this feature on this platform. -For example, Linux and Windows have mmap'ed files, and APR is providing an -interface for mmapp'ing a file. On both Linux and Windows, APR_HAS_MMAP -should evaluate to one, and the ap_mmap_* functions should map files into -memory and return the appropriate status codes.</p> - -<p>If your OS of choice does not have mmap'ed files, APR_HAS_MMAP should -evaluate to zero, and all ap_mmap_* functions should not be defined. The -second step is a precaution that will allow us to break at compile time if a -programmer tries to use unsupported functions.</p> - -<h2>APR types</h2> - -<p>The base types in APR</p> - -<ul> -<li>dso<br> - Shared library routines -<li>mmap<br> - Memory-mapped files -<li>poll<br> - Polling I/O -<li>time<br> - Time -<li>user<br> - Users and groups -<li>locks<br> - Process and thread locks (critical sections) -<li>shmem<br> - Shared memory -<li>file_io<br> - File I/O, including pipes -<li>atomic<br> - Atomic integer operations -<li>strings<br> - String handling routines -<li>memory<br> - Pool-based memory allocation -<li>passwd<br> - Reading passwords from the terminal -<li>tables<br> - Tables and hashes -<li>network_io<br> - Network I/O -<li>threadproc<br> - Threads and processes -<li>misc<br> - Any APR type which doesn't have any other place to belong. This - should be used sparingly. -<li>support<br> - Functions meant to be used across multiple APR types. This area - is for internal functions only. If a function is exposed, it should - not be put here. -</ul> - -<h2>Directory Structure</h2> - -<p>Each type has a base directory. Inside this base directory, are -subdirectories, which contain the actual code. These subdirectories are named -after the platforms the are compiled on. Unix is also used as a common -directory. If the code you are writing is POSIX based, you should look at the -code in the unix directory. A good rule of thumb, is that if more than half -your code needs to be ifdef'ed out, and the structures required for your code -are substantively different from the POSIX code, you should create a new -directory.</p> - -<p>Currently, the APR code is written for Unix, BeOS, Windows, and OS/2. An -example of the directory structure is the file I/O directory:</p> - -<pre> -apr - | - -> file_io - | - -> unix The Unix and common base code - | - -> win32 The Windows code - | - -> os2 The OS/2 code -</pre> - -<p>Obviously, BeOS does not have a directory. This is because BeOS is currently -using the Unix directory for it's file_io.</p> - -<p>There are a few special top level directories. These are test and include. -Test is a directory which stores all test programs. It is expected -that if a new type is developed, there will also be a new test program, to -help people port this new type to different platforms. A small document -describing how to create new tests that integrate with the test suite can be -found in the test/ directory. Include is a directory which stores all -required APR header files for external use.</p> - -<h2>Creating an APR Type</h2> - -<p>The current design of APR requires that most APR types be incomplete. -It is not possible to write flexible portable code if programs can access -the internals of APR types. This is because different platforms are -likely to define different native types. There are only two execptions to -this rule:</p> - -<ul> -<li>The first exception to this rule is if the type can only reasonably be -implemented one way. For example, time is a complete type because there -is only one reasonable time implementation. - -<li>The second exception to the incomplete type rule can be found in -apr_portable.h. This file defines the native types for each platform. -Using these types, it is possible to extract native types for any APR type.</p> -</ul> - -<p>For this reason, each platform defines a structure in their own directories. -Those structures are then typedef'ed in an external header file. For example -in file_io/unix/fileio.h:</p> - -<pre> - struct ap_file_t { - apr_pool_t *cntxt; - int filedes; - FILE *filehand; - ... - } -</pre> - -<p>In include/apr_file_io.h:</p> - </pre> - typedef struct ap_file_t ap_file_t; - </pre> - -<p> This will cause a compiler error if somebody tries to access the filedes -field in this structure. Windows does not have a filedes field, so obviously, -it is important that programs not be able to access these.</p> - -<p>You may notice the apr_pool_t field. Most APR types have this field. This -type is used to allocate memory within APR. Because every APR type has a pool, -any APR function can allocate memory if it needs to. This is very important -and it is one of the reasons that APR works. If you create a new type, you -must add a pool to it. If you do not, then all functions that operate on that -type will need a pool argument.</p> - -<h2>New Function</h2> - -<p>When creating a new function, please try to adhere to these rules.</p> - -<ul> -<li> Result arguments should be the first arguments. -<li> If a function needs a pool, it should be the last argument. -<li> These rules are flexible, especially if it makes the code easier - to understand because it mimics a standard function. -</ul> - -<h2>Documentation</h2> - -<p>Whenever a new function is added to APR, it MUST be documented. New -functions will not be committed unless there are docs to go along with them. -The documentation should be a comment block above the function in the header -file.</p> - -<p>The format for the comment block is:</p> - -<pre> - /** - * Brief description of the function - * @param parma_1_name explanation - * @param parma_2_name explanation - * @param parma_n_name explanation - * @tip Any extra information people should know. - * @deffunc function prototype if required - */ -</pre> - -<p>For an actual example, look at any file in the include directory. The -reason the docs are in the header files is to ensure that the docs always -reflect the current code. If you change paramters or return values for a -function, please be sure to update the documentation.</p> - -<h2>APR Error reporting</h2> - -<p>Most APR functions should return an ap_status_t type. The only time an -APR function does not return an ap_status_t is if it absolutely CAN NOT -fail. Examples of this would be filling out an array when you know you are -not beyond the array's range. If it cannot fail on your platform, but it -could conceivably fail on another platform, it should return an ap_status_t. -Unless you are sure, return an ap_status_t.</p> - -<strong> - This includes functions that return TRUE/FALSE values. How that - is handled is discussed below -</strong> - -<p>All platforms return errno values unchanged. Each platform can also have -one system error type, which can be returned after an offset is added. -There are five types of error values in APR, each with it's own offset.</p> - -<!-- This should be turned into a table, but I am lazy today --> -<pre> - Name Purpose -0) This is 0 for all platforms and isn't really defined - anywhere, but it is the offset for errno values. - (This has no name because it isn't actually defined, - but for completeness we are discussing it here). - -1) APR_OS_START_ERROR This is platform dependent, and is the offset at which - APR errors start to be defined. Error values are - defined as anything which caused the APR function to - fail. APR errors in this range should be named - APR_E* (i.e. APR_ENOSOCKET) - -2) APR_OS_START_STATUS This is platform dependent, and is the offset at which - APR status values start. Status values do not indicate - success or failure, and should be returned if - APR_SUCCESS does not make sense. APR status codes in - this range should be name APR_* (i.e. APR_DETACH) - -4) APR_OS_START_USEERR This is platform dependent, and is the offset at which - APR apps can begin to add their own error codes. - -3) APR_OS_START_SYSERR This is platform dependent, and is the offset at which - system error values begin. -</pre> - -<strong>The difference in naming between APR_OS_START_ERROR and -APR_OS_START_STATUS mentioned above allows programmers to easily determine if -the error code indicates an error condition or a status codition.</strong> - -<p>If your function has multiple return codes that all indicate success, but -with different results, or if your function can only return PASS/FAIL, you -should still return an apr_status_t. In the first case, define one -APR status code for each return value, an example of this is -<code>apr_proc_wait</code>, which can only return APR_CHILDDONE, -APR_CHILDNOTDONE, or an error code. In the second case, please return -APR_SUCCESS for PASS, and define a new APR status code for failure, an -example of this is <code>apr_compare_users</code>, which can only return -APR_SUCCESS, APR_EMISMATCH, or an error code.</p> - -<p>All of these definitions can be found in apr_errno.h for all platforms. When -an error occurs in an APR function, the function must return an error code. -If the error occurred in a system call and that system call uses errno to -report an error, then the code is returned unchanged. For example: </p> - -<pre> - if (open(fname, oflags, 0777) < 0) - return errno; -</pre> - -<p>The next place an error can occur is a system call that uses some error value -other than the primary error value on a platform. This can also be handled -by APR applications. For example:</p> - -<pre> - if (CreateFile(fname, oflags, sharemod, NULL, - createflags, attributes, 0) == INVALID_HANDLE_VALUE - return (GetLAstError() + APR_OS_START_SYSERR); -</pre> - -<p>These two examples implement the same function for two different platforms. -Obviously even if the underlying problem is the same on both platforms, this -will result in two different error codes being returned. This is OKAY, and -is correct for APR. APR relies on the fact that most of the time an error -occurs, the program logs the error and continues, it does not try to -programatically solve the problem. This does not mean we have not provided -support for programmatically solving the problem, it just isn't the default -case. We'll get to how this problem is solved in a little while.</p> - -<p>If the error occurs in an APR function but it is not due to a system call, -but it is actually an APR error or just a status code from APR, then the -appropriate code should be returned. These codes are defined in apr_errno.h -and should be self explanatory.</p> - -<p>No APR code should ever return a code between APR_OS_START_USEERR and -APR_OS_START_SYSERR, those codes are reserved for APR applications.</p> - -<p>To programmatically correct an error in a running application, the error -codes need to be consistent across platforms. This should make sense. APR -has provided macros to test for status code equivalency. For example, to -determine if the code that you received from the APR function means EOF, you -would use the macro APR_STATUS_IS_EOF().</p> - -<p>Why did APR take this approach? There are two ways to deal with error -codes portably.</p> - -<ol type=1> -<li> Return the same error code across all platforms. -<li> Return platform specific error codes and convert them when necessary. -</ol> - -<p>The problem with option number one is that it takes time to convert error -codes to a common code, and most of the time programs want to just output -an error string. If we convert all errors to a common subset, we have four -steps to output an error string:</p> - -<p>The seocnd problem with option 1, is that it is a lossy conversion. For -example, Windows and OS/2 have a couple hundred error codes, but POSIX errno -only defines about 50 errno values. This means that if we convert to a -canonical error value immediately, there is no way for the programmer to -get the actual system error.</p> - -<pre> - make syscall that fails - convert to common error code step 1 - return common error code - check for success - call error output function step 2 - convert back to system error step 3 - output error string step 4 -</pre> - -<p>By keeping the errors platform specific, we can output error strings in two -steps.</p> - -<pre> - make syscall that fails - return error code - check for success - call error output function step 1 - output error string step 2 -</pre> - -<p>Less often, programs change their execution based on what error was returned. -This is no more expensive using option 2 than it is using option 1, but we -put the onus of converting the error code on the programmer themselves. -For example, using option 1:</p> - -<pre> - make syscall that fails - convert to common error code - return common error code - decide execution based on common error code -</pre> - -<p>Using option 2:</p> - -<pre> - make syscall that fails - return error code - convert to common error code (using ap_canonical_error) - decide execution based on common error code -</pre> - -<p>Finally, there is one more operation on error codes. You can get a string -that explains in human readable form what has happened. To do this using -APR, call ap_strerror().</p> - |