175 lines
6.0 KiB
HTML
175 lines
6.0 KiB
HTML
<html>
|
|
<head>
|
|
<title>libsm Overview</title>
|
|
</head>
|
|
<body>
|
|
|
|
<center>
|
|
<h1> libsm Overview </h1>
|
|
<br> $Id: index.html,v 1.14 2001/02/13 21:21:25 gshapiro Exp $
|
|
</center>
|
|
|
|
<h2> Introduction </h2>
|
|
|
|
Libsm is a library of generally useful C abstractions.
|
|
Libsm stands alone; it depends on no other sendmail libraries,
|
|
and the only sendmail header files it depends on are its own,
|
|
which reside in <tt>../include/sm</tt>.
|
|
|
|
<h2> Contents </h2>
|
|
|
|
Here is the current set of packages:
|
|
<blockquote>
|
|
<a href="gen.html"> gen: general definitions </a><br>
|
|
<a href="debug.html"> debug: debugging and tracing </a><br>
|
|
<a href="assert.html"> assert: assertion handling and aborts </a><br>
|
|
<a href="heap.html"> heap: memory allocation </a><br>
|
|
<a href="exc.html"> exc: exception handling </a><br>
|
|
<a href="rpool.html"> rpool: resource pools </a><br>
|
|
<a href="cdefs.html"> cdefs: C language portability macros </a><br>
|
|
<a href="io.html"> io: buffered i/o </a><br>
|
|
</blockquote>
|
|
|
|
<h2> Naming Conventions </h2>
|
|
|
|
Some of the symbols defined by libsm
|
|
come from widely used defacto or dejure standards.
|
|
Examples include <tt>size_t</tt> (from the C 89 standard),
|
|
<tt>bool</tt> (from the C 99 standard),
|
|
<tt>strerror</tt> (from Posix),
|
|
and <tt>__P</tt> (from BSD and Linux).
|
|
In these cases, we use the standard name rather than
|
|
inventing a new name.
|
|
We import the name from the appropriate header file when possible,
|
|
or define it ourselves when necessary.
|
|
When you are using one of these abstractions, you must include
|
|
the appropriate libsm header file.
|
|
For example, when you are using <tt>strerror</tt>, you must
|
|
include <tt><sm/string.h></tt> instead of <tt><string.h></tt>.
|
|
|
|
<p>
|
|
When we aren't implementing a standard interface,
|
|
we use a naming convention that attempts to maximize portability
|
|
across platforms, and minimize conflicts with other libraries.
|
|
Except for a few seemingly benign exceptions,
|
|
all names begin with <tt>SM_</tt>, <tt>Sm</tt> or <tt>sm_</tt>.
|
|
|
|
<p>
|
|
The ISO C, Posix and Unix standards forbid applications
|
|
from using names beginning with <tt>__</tt> or <tt>_[A-Z]</tt>,
|
|
and place restrictions on what sorts of names can begin
|
|
with <tt>_[a-z]</tt>. Such names are reserved for the compiler and
|
|
the standard libraries.
|
|
For this reason, we avoid defining any names that begin
|
|
with <tt>_</tt>.
|
|
For example, all libsm header file idempotency macros have the form
|
|
<tt>SM_FOO_H</tt> (no leading <tt>_</tt>).
|
|
|
|
<p>
|
|
Type names begin with <tt>SM_</tt> and end with <tt>_T</tt>.
|
|
Note that the Posix standard reserves all identifiers ending
|
|
with <tt>_t</tt>.
|
|
|
|
<p>
|
|
All functions that are capable of raising an exception
|
|
have names ending in <tt>_x</tt>, and developers are
|
|
encouraged to use this convention when writing new code.
|
|
This naming convention may seem unnecessary at first,
|
|
but it becomes extremely useful during maintenance,
|
|
when you are attempting to reason about the correctness
|
|
of a block of code,
|
|
and when you are trying to track down exception-related bugs
|
|
in existing code.
|
|
|
|
<h2> Coding Conventions </h2>
|
|
|
|
The official style for function prototypes in libsm header files is
|
|
|
|
<blockquote><pre>
|
|
extern int
|
|
foo __P((
|
|
int _firstarg,
|
|
int _secondarg));
|
|
</pre></blockquote>
|
|
|
|
The <tt>extern</tt> is useless, but required for stylistic reasons.
|
|
The parameter names are optional; if present they are lowercase
|
|
and begin with _ to avoid namespace conflicts.
|
|
Each parameter is written on its own line to avoid very long lines.
|
|
|
|
<p>
|
|
For each structure <tt>struct sm_foo</tt> defined by libsm,
|
|
there is a typedef:
|
|
|
|
<blockquote><pre>
|
|
typedef struct sm_foo SM_FOO_T;
|
|
</pre></blockquote>
|
|
|
|
and there is a global variable which is defined as follows:
|
|
|
|
<blockquote><pre>
|
|
const char SmFooMagic[] = "sm_foo";
|
|
</pre></blockquote>
|
|
|
|
The first member of each structure defined by libsm is
|
|
|
|
<blockquote><pre>
|
|
const char *sm_magic;
|
|
</pre></blockquote>
|
|
|
|
For all instances of <tt>struct sm_foo</tt>,
|
|
<tt>sm_magic</tt> contains <tt>SmFooMagic</tt>,
|
|
which points to a unique character string naming the type.
|
|
It is used for debugging and run time type checking.
|
|
|
|
<p>
|
|
Each function with a parameter declared <tt>SM_FOO_T *foo</tt>
|
|
contains the following assertion:
|
|
|
|
<blockquote><pre>
|
|
SM_REQUIRE_ISA(foo, SmFooMagic);
|
|
</pre></blockquote>
|
|
|
|
which is equivalent to
|
|
|
|
<blockquote><pre>
|
|
SM_REQUIRE(foo != NULL && foo->sm_magic == SmFooMagic);
|
|
</pre></blockquote>
|
|
|
|
When an object of type <tt>SM_FOO_T</tt> is deallocated,
|
|
the member <tt>sm_magic</tt> is set to <tt>NULL</tt>.
|
|
That will cause the above assertion to fail if a dangling pointer is used.
|
|
|
|
<h2> Additional Design Goals </h2>
|
|
|
|
Here are some of my design goals:
|
|
<ul>
|
|
<p>
|
|
<li>The sm library is self contained; it does not depend on any other
|
|
sendmail libraries or header files.
|
|
<p>
|
|
<li>The sm library must be compatible with shared libraries,
|
|
even on platforms with weird implementation restrictions.
|
|
I assume that a shared library can export global variables;
|
|
the debug package relies on this assumption.
|
|
I do not assume that if an application redefines a function defined
|
|
in a shared library, the shared library will use the version of the
|
|
function defined in the application in preference to the version
|
|
that it defines.
|
|
For this reason, I provide interfaces for registering handler functions
|
|
in cases where an application might need to override standard behaviour.
|
|
<p>
|
|
<li>The sm library must be compatible with threads.
|
|
The debug package presents a small problem: I don't want
|
|
sm_debug_active to acquire and release a lock.
|
|
So I assume that
|
|
there exists an integral type <tt>SM_ATOMIC_INT_T</tt>
|
|
(see <a href="gen.html"><tt><sm/gen.h></tt></a>)
|
|
that can be accessed and updated atomically.
|
|
I assume that locking must be used to guard updates and accesses to
|
|
any other type, and I have designed the interfaces accordingly.
|
|
</ul>
|
|
|
|
</body>
|
|
</html>
|