19 Sep
2017
19 Sep
'17
7:53 p.m.
Larry McVoy <lm(a)mcvoy.com> wrote:
|On Mon, Sep 18, 2017 at 08:52:08PM -0400, Random832 wrote:
|> On Thu, Sep 14, 2017, at 15:37, Steve Johnson wrote:
|>> I wrote a paper on error messages at one point.?? I had examples from
|>> bad to best.?? In a nutshell (worst to best):
|>>
|>> * <program aborts, leaving the world in an unknown state>
|>> * "internal error",?? "beta table overflow",
"operation failed"
|>> * "Writing the output file failed"
|>> * "File xxx could not be opened for writing."
|>> * "File xxx could not be opened for writing: check the file location
|>> and permissions"
|>>
|>> * "Writing the output file xxx caused an error.?? See <link> for
|>> possible reasons and corrections"
|>>
|>> Most git messages fall between 2 and 3.?? But there are occasional 4's
|>> and 5's.
|>
|> Just out of curiosity, where does perror(filename), quite possibly the
|> *most* common error message on Unix as a whole, fall on your scale? It
|> says which of the file location or permissions (or whatever else) it is,
|> but not whether it was attempting to open it for reading or writing.
|
|So in the BitKeeper source, perror is redifined to my_perror which is
|this:
|
|void
|my_perror(char *file, int line, char *msg)
|{
| char *p = 0;
| int save = errno;
|
| if (p = getenv("_BK_VERSION")) {
| if (strneq(p, "bk-", 3)) p += 3;
| fprintf(stderr, "%s:%d (%s): ", file, line, p);
|} else {
| fprintf(stderr, "%s:%d: ", file, line);
|}
| if (p = strerror(errno)) {
| fprintf(stderr, "%s: %s\n", msg, p);
|} else {
| fprintf(stderr, "%s: errno=%d\n", msg, errno);
|}
| errno = save;
|}
|
|libc should do that.
That really made me wonder why "save" is not used, errno may
eventually change along the way. Ok ok, but.. well.
I have had a Txt::FormatEncoder which was the sole implementation
of a format codec (plus FormatDecoder), which supported %m
* "%m"
* Print the description of the \SF Errno which was active at setup() time,
* if it's value has an assigned description
* (otherwise a message is printed which says that this value is unknown).
* This always prints the original english string \ldots
mostly for debugging and developers thus, but why not, except for
inter-dependencies, thus optional at least, support of
a # modifier could have been added.
The encoder could be used for finite (CP::) as well as resizable
buffers (CString, ([Sys::]IO::TextWriter, etc.) as in
static void _MyAddVFmt(
CString &_str,
const char *_fmt,
void *_valist)
{
ui32 grow, olen;
auto Txt::FormatEncoder fe;
// use special case+update() for better code flow
(void)fe.setup(NIL, 0, _fmt, _valist);
for(grow=80-1; ; ) {
olen = _str.length();
(void)fe.update(_str.reserve(grow).data()+olen, grow)
.call();
// resize insufficient? nothing changed!
if(fe.isInsufficient()) {
(void)_str.truncate(olen);
grow <<= 1;
} else {
(void)_str.truncate(olen + fe.count());
if(fe.isFinished())
break;
grow = 80-1;
}
}
return;
}
Terrible: no overflow protection. And camel case.
Plus a [Sys::]Log and [Sys::]Log::Domain with vWrite() and
pub static void write(Priority _prio, const char *_fmt, ...);
That was for the builtin Domain only, which needs to be created
to overcome the no-op state, optionally SMP safe:
pub static void createBuiltinDomain(IO::Device *_dev,
SMP::Mutex *_mtx=NIL);
pub static Domain *getBuiltinDomain(void){ return(s_bdom); }
Optionally in [Sys::]POSIX there also was
pub static Log::Domain *createSyslogDomain(
SyslogFacility _facility=user,
boolean _includepid=tru1,
const char *_intro=NIL,
boolean _enabled=tru1,
Log::Priority _prio=Log::debug);
but that cannot be used as the main log domain. I have forgotten
why. It also used a shared internal socket connection and mutex
for all domains created like that, but can (re)use
CP::fromVFormat() to actually prepare the written messages in
the 1 KB stack buffer for syslog purposes. At least. All this of
course very inconvenient in a main():
Mem::Cache::enableStatistics();
Mem::Cache::configure(Mem::Cache::conf_trash, tru1);
Std::createChannels(tru1, tru1, tru1);
No standard streams by default.
Log::setEnabled(tru1);
Log::setPriority(Log::debug);
Log::createBuiltinDomain(Std::ferr);
No logging by default.
(void)Misc::NYD::setDumpChannel(Std::ferr);
And NotYetDead chirps or profiling needs to be charged, too.
But despite all faulty design decisions, implementation
shortcomings, missing focus on security details, etc., at least
you can exactly specify what is going on. And get that and
nothing else.
Unfortunately C++ has become overly huge, and i am not rich enough
to go for a C+ / C-- / C-w-C. Well. There is i think a German
who did something i think nice, Python style source code,
transformed to C which then is compilable as such. But with
garbage collection and all that stuff that interpreted languages
ship, and inclusive a runtime. Now called Nim, Nimrod no longer.
I have just looked, in the meantime also compiles to JavaScript.
Getting real grip it seems, on github etc. Well. Never used it,
but sounds very interesting to me.
The NetBSD getenv() uses a fast tree i think to speed up lookups.
I think especially in massive parallel object-based programs any
sort of perror() is likely overchallenged and needs to attach to
more context. Then again i have no idea better than "CTX1: CTX2:
CTX3: message" either, and always get a headache when i see
OpenSSL error messages which exactly go this route. So you need
two programs, one to do the work, and the other to interpret the
error messages of the first...
--steffen
|
|Der Kragenbaer, The moon bear,
|der holt sich munter he cheerfully and one by one
|einen nach dem anderen runter wa.ks himself off
|(By Robert Gernhardt)