From e8ec7aa8e38a93f5b034ac74cebce5de23710317 Mon Sep 17 00:00:00 2001 From: hongbotian Date: Mon, 30 Nov 2015 01:45:08 -0500 Subject: upload http JIRA: BOTTLENECK-10 Change-Id: I7598427ff904df438ce77c2819ee48ac75ffa8da Signed-off-by: hongbotian --- .../httpd-2.0.64/srclib/apr/docs/APRDesign.html | 399 +++++++++++++++++++++ 1 file changed, 399 insertions(+) create mode 100644 rubbos/app/httpd-2.0.64/srclib/apr/docs/APRDesign.html (limited to 'rubbos/app/httpd-2.0.64/srclib/apr/docs/APRDesign.html') 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 new file mode 100644 index 00000000..7d1caeb8 --- /dev/null +++ b/rubbos/app/httpd-2.0.64/srclib/apr/docs/APRDesign.html @@ -0,0 +1,399 @@ + +APR Design Document + +

Design of APR

+ +

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.

+ +

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.

+ +

This document will discuss the structure of APR, and how best to contribute +code to the effort.

+ +

APR On Windows and Netware

+ +

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.

+ +

+ 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. +

+ +

APR Features

+ +

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.

+ +

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:

+ +APR_HAS_FEATURE + +

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.

+ +

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.

+ +

APR types

+ +

The base types in APR

+ + + +

Directory Structure

+ +

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.

+ +

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:

+ +
+apr
+  |
+   ->  file_io
+          |
+           -> unix            The Unix and common base code
+          |
+           -> win32           The Windows code
+          | 
+           -> os2             The OS/2 code
+
+ +

Obviously, BeOS does not have a directory. This is because BeOS is currently +using the Unix directory for it's file_io.

+ +

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.

+ +

Creating an APR Type

+ +

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:

+ + + +

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:

+ +
+    struct ap_file_t {
+        apr_pool_t *cntxt;
+        int filedes;
+        FILE *filehand;
+        ...
+    }
+
+ +

In include/apr_file_io.h:

+ + typedef struct ap_file_t ap_file_t; + + +

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.

+ +

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.

+ +

New Function

+ +

When creating a new function, please try to adhere to these rules.

+ + + +

Documentation

+ +

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.

+ +

The format for the comment block is:

+ +
+    /**
+     * 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
+     */ 
+
+ +

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.

+ +

APR Error reporting

+ +

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.

+ + + This includes functions that return TRUE/FALSE values. How that + is handled is discussed below + + +

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.

+ + +
+    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.
+
+ +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. + +

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 +apr_proc_wait, 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 apr_compare_users, which can only return +APR_SUCCESS, APR_EMISMATCH, or an error code.

+ +

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:

+ +
+    if (open(fname, oflags, 0777) < 0)
+        return errno;
+
+ +

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:

+ +
+    if (CreateFile(fname, oflags, sharemod, NULL, 
+                   createflags, attributes, 0) == INVALID_HANDLE_VALUE
+        return (GetLAstError() + APR_OS_START_SYSERR);
+
+ +

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.

+ +

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.

+ +

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.

+ +

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().

+ +

Why did APR take this approach? There are two ways to deal with error +codes portably.

+ +
    +
  1. Return the same error code across all platforms. +
  2. Return platform specific error codes and convert them when necessary. +
+ +

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:

+ +

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.

+ +
+    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
+
+ +

By keeping the errors platform specific, we can output error strings in two +steps.

+ +
+    make syscall that fails
+        return error code
+            check for success
+            call error output function               step 1
+                output error string                  step 2
+
+ +

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:

+ +
+    make syscall that fails
+        convert to common error code
+        return common error code
+            decide execution based on common error code
+
+ +

Using option 2:

+ +
+    make syscall that fails
+        return error code
+            convert to common error code (using ap_canonical_error)
+            decide execution based on common error code
+
+ +

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().

+ -- cgit