1. proposal EDS functions
Hello,
I regularly use EDS in my projects for quite a few years now.
Whenever I start a new project I found myself rewritting these
functions. I suggest to include them in the standard database.e
file.
Any comment, support, improvment is welcome. I suppose all of us
developed some similar rountines...
global function db_startup(sequence dbf)
integer err,lock
lock=DB_LOCK_NO
err=db_open(dbf,lock)
if err=DB_OK then
return DB_OK
elsif err=DB_OPEN_FAIL then
return db_create(dbf,lock)
elsif err=DB_LOCK_FAIL then
for i=1 to 10 by 1 do
if db_open(dbf,lock)=DB_OK then
return DB_OK
else
sleep(2)
end if
end for
return DB_LOCK_FAIL
else
return DB_OPEN_FAIL
end if
end function
global function db_startup_table(sequence t)
integer err
if db_select_table(t)=DB_OK
or db_create_table(t)=DB_OK
then
return DB_OK
end if
return DB_OPEN_FAIL
end function
Regards,
Salix
2. Re: proposal EDS functions
Salix wrote:
>
> Hello,
>
> I regularly use EDS in my projects for quite a few years now.
> Whenever I start a new project I found myself rewritting these
> functions. I suggest to include them in the standard database.e
> file.
>
> Any comment, support, improvment is welcome. I suppose all of us
> developed some similar rountines...
>
> }}}
<eucode>
> global function db_startup(sequence dbf)
> integer err,lock
> lock=DB_LOCK_NO
> err=db_open(dbf,lock)
> if err=DB_OK then
> return DB_OK
> elsif err=DB_OPEN_FAIL then
> return db_create(dbf,lock)
> elsif err=DB_LOCK_FAIL then
> for i=1 to 10 by 1 do
> if db_open(dbf,lock)=DB_OK then
> return DB_OK
> else
> sleep(2)
> end if
> end for
> return DB_LOCK_FAIL
> else
> return DB_OPEN_FAIL
> end if
> end function
>
> global function db_startup_table(sequence t)
> integer err
> if db_select_table(t)=DB_OK
> or db_create_table(t)=DB_OK
> then
> return DB_OK
> end if
> return DB_OPEN_FAIL
> end function
> </eucode>
{{{
>
> Regards,
>
> Salix
just to add to this post... here is a database.e "function" only handler that i
use alot...
include database.e
------------------
global
procedure dbase(sequence s, object x, integer c)
x = call_func(routine_id(s),x)
if x != DB_OK and x != c -- continue
then
clear_screen()
puts (1,"\ndbase() -> A fatal database failure...\n")
-- Todo: display s & x
abort(x)
end if
end procedure
* execution continues if the return error is DB_OK or the
allowed condition, else a fatal error is reported...
-- example:
-- select a table from the database, execution will countinue if
-- DB_OK or DB_OPEN_FAIL
dbase("db_select_table",{"my_table"},DB_OPEN_FAIL)
-- create a table in the database, execution will continue if
-- DB_OK or DB_EXISTS_ALREADY
dbase("db_create_table",{"my_table"},DB_EXISTS_ALREADY)
3. Re: proposal EDS functions
Salix wrote:
>
> Hello,
>
> I regularly use EDS in my projects for quite a few years now.
> Whenever I start a new project I found myself rewritting these
> functions. I suggest to include them in the standard database.e
> file.
>
> Any comment, support, improvment is welcome. I suppose all of us
> developed some similar rountines...
>
I can see some issues with the below function:
> }}}
<eucode>
> global function db_startup(sequence dbf)
> integer err,lock
> lock=DB_LOCK_NO
> err=db_open(dbf,lock)
> if err=DB_OK then
> return DB_OK
> elsif err=DB_OPEN_FAIL then
> return db_create(dbf,lock)
> elsif err=DB_LOCK_FAIL then
> for i=1 to 10 by 1 do
> if db_open(dbf,lock)=DB_OK then
> return DB_OK
> else
> sleep(2)
> end if
> end for
> return DB_LOCK_FAIL
> else
> return DB_OPEN_FAIL
> end if
> end function
>
1/ I assume lock is an argument to the function, not a local variable as you
coded it;
2/ I'd expect the "10" to be adjustable. This would require defining a
db_max_retry global variable, some factory default for it and a procedure to
reset it to that default. Also, you may wish to have a setter which guards
against invalid/undesirably large values. It is ok as long as you are admin of
your database; if you are not, you should not even be allowed to set that number.
3/ Same remarks as above regarding the delay between consecutive retries (the
"2"). Replace "large" by "small" though.
4/ Additionally, your method is blocking, as you sleep() between retries, even
though some systems will enable you to yield immediately and be notified of I/O
success or timeout. I think db_startup() should try to use these mechanisms where
available. They don't exist under DOS, do under Windows 2K and later. Not sure
for NT, not available under 9x I think. For unixes, I have no clue.
Also, see the thread about nonblocking I/O in Eu.
Btw, I never tried mixing Windows' waitable I/O objects and Eu tasks. No idea
whether it works without too much effort. I guess the trick is for the callback
to call Eu's scheduler with the id of a suspended task which will act real-time
upon notification.
> global function db_startup_table(sequence t)
> integer err
> if db_select_table(t)=DB_OK
> or db_create_table(t)=DB_OK
> then
> return DB_OK
> end if
> return DB_OPEN_FAIL
> end function
> </eucode>
{{{
>
No objection there. However, returning a new DB_CREATED status code when the
table didn't exist prior could provide useful information (for instance, do some
init job if the table wasn't there before). Returning DB_CREATED would be useful
in db_startup() too.
CChris
> Regards,
>
> Salix
