Re: MODERATOR WARNING Re: [GENERAL] Exception Handling in C-Language Functions?

2012-12-03 Thread David Fetter 
OK :)

Is there a way to do this automatically?

Cheers,
David.
On Mon, Dec 03, 2012 at 03:14:54AM -0300, Alvaro Herrera wrote:
 MODERATOR WARNING
 
 I noticed that this guy Rahul seems to be reinjecting old list emails
 somehow.  Please don't approve anything coming from him.  Observe this
 example:
 
 http://postgresql.1045698.n5.nabble.com/Re-GENERAL-MS-Access-and-Stored-procedures-td1843848.html
 http://postgresql.1045698.n5.nabble.com/Re-GENERAL-MS-Access-and-Stored-procedures-td5734652.html
 The original message was posted in 2005!
 
 The message here is this one (also in 2005):
 http://postgresql.1045698.n5.nabble.com/GENERAL-Exception-Handling-in-C-Language-Functions-td1843896.html
 
 I have no idea what's going on.  Maybe it's something to do with Nabble.
 There are others pending moderation in pgsql-admin and pgsql-hackers too.
 
 rahul143 wrote:
  I have the created a C-Language function (code is below).  Now, I 
  wonder: How do I handle exceptions, for example if malloc cannot assign 
  the necessary memory?  Do palloc and pfree handle such a case 
  cleanly?  Should I simply use an assert? 
  
  #include postgres.h 
  #include string.h 
  #include stdlib.h 
  #include fmgr.h 
  #include libinn.h 
  
  PG_FUNCTION_INFO_V1(ffiinews_uwildmat); 
  
  /* Wrapper for INN's function uwildmat.  Needs parameters in UTF-8. */ 
  Datum ffiinews_uwildmat(PG_FUNCTION_ARGS) { 
  VarChar *text = PG_GETARG_VARCHAR_P(0); 
  VarChar *pattern = PG_GETARG_VARCHAR_P(1); 
  int text_len = VARSIZE(text)-VARHDRSZ; 
  int pattern_len = VARSIZE(pattern)-VARHDRSZ; 
  char *tmp_text = (char *)malloc(text_len+1); 
  if (tmp_text == NULL) 
  ; /* What now? */ 
  char *tmp_pattern = (char *)malloc(pattern_len+1); 
  if (tmp_pattern == NULL) 
  ; /* What now? */ 
  strncpy(tmp_text, VARDATA(text), text_len); 
  tmp_text[text_len] = '\0'; 
  strncpy(tmp_pattern, VARDATA(pattern), pattern_len); 
  tmp_pattern[pattern_len] = '\0'; 
  bool matches = uwildmat(tmp_text, tmp_pattern); 
  
  
  
  -
  
  
  
  
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 PostgreSQL Development, 24x7 Support, Training  Services

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Re: [GENERAL] Exception Handling in C-Language Functions?

2012-12-03 Thread Merlin Moncure 
On Sun, Dec 2, 2012 at 11:18 PM, rahul143 rk204...@gmail.com wrote:
 I have the created a C-Language function (code is below).  Now, I
 wonder: How do I handle exceptions, for example if malloc cannot assign
 the necessary memory?  Do palloc and pfree handle such a case
 cleanly?  Should I simply use an assert?

 #include postgres.h
 #include string.h
 #include stdlib.h
 #include fmgr.h
 #include libinn.h

 PG_FUNCTION_INFO_V1(ffiinews_uwildmat);

 /* Wrapper for INN's function uwildmat.  Needs parameters in UTF-8. */
 Datum ffiinews_uwildmat(PG_FUNCTION_ARGS) {
 VarChar *text = PG_GETARG_VARCHAR_P(0);
 VarChar *pattern = PG_GETARG_VARCHAR_P(1);
 int text_len = VARSIZE(text)-VARHDRSZ;
 int pattern_len = VARSIZE(pattern)-VARHDRSZ;
 char *tmp_text = (char *)malloc(text_len+1);
 if (tmp_text == NULL)
 ; /* What now? */
 char *tmp_pattern = (char *)malloc(pattern_len+1);
 if (tmp_pattern == NULL)
 ; /* What now? */
 strncpy(tmp_text, VARDATA(text), text_len);
 tmp_text[text_len] = '\0';
 strncpy(tmp_pattern, VARDATA(pattern), pattern_len);
 tmp_pattern[pattern_len] = '\0';
 bool matches = uwildmat(tmp_text, tmp_pattern);

yes, you should always use database memory api: palloc/pfree and if
necessary memory context switching.  memory allocation error then
raises database exception.  any situation that raises an exception or
other critical needs to be caught and rethrown as database exception
(ereport, etc).

merlin


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[GENERAL] Exception Handling in C-Language Functions?

2012-12-02 Thread rahul143 
I have the created a C-Language function (code is below).  Now, I 
wonder: How do I handle exceptions, for example if malloc cannot assign 
the necessary memory?  Do palloc and pfree handle such a case 
cleanly?  Should I simply use an assert? 

#include postgres.h 
#include string.h 
#include stdlib.h 
#include fmgr.h 
#include libinn.h 

PG_FUNCTION_INFO_V1(ffiinews_uwildmat); 

/* Wrapper for INN's function uwildmat.  Needs parameters in UTF-8. */ 
Datum ffiinews_uwildmat(PG_FUNCTION_ARGS) { 
VarChar *text = PG_GETARG_VARCHAR_P(0); 
VarChar *pattern = PG_GETARG_VARCHAR_P(1); 
int text_len = VARSIZE(text)-VARHDRSZ; 
int pattern_len = VARSIZE(pattern)-VARHDRSZ; 
char *tmp_text = (char *)malloc(text_len+1); 
if (tmp_text == NULL) 
; /* What now? */ 
char *tmp_pattern = (char *)malloc(pattern_len+1); 
if (tmp_pattern == NULL) 
; /* What now? */ 
strncpy(tmp_text, VARDATA(text), text_len); 
tmp_text[text_len] = '\0'; 
strncpy(tmp_pattern, VARDATA(pattern), pattern_len); 
tmp_pattern[pattern_len] = '\0'; 
bool matches = uwildmat(tmp_text, tmp_pattern); 



-




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MODERATOR WARNING Re: [GENERAL] Exception Handling in C-Language Functions?

2012-12-02 Thread Alvaro Herrera 
MODERATOR WARNING

I noticed that this guy Rahul seems to be reinjecting old list emails
somehow.  Please don't approve anything coming from him.  Observe this
example:

http://postgresql.1045698.n5.nabble.com/Re-GENERAL-MS-Access-and-Stored-procedures-td1843848.html
http://postgresql.1045698.n5.nabble.com/Re-GENERAL-MS-Access-and-Stored-procedures-td5734652.html
The original message was posted in 2005!

The message here is this one (also in 2005):
http://postgresql.1045698.n5.nabble.com/GENERAL-Exception-Handling-in-C-Language-Functions-td1843896.html

I have no idea what's going on.  Maybe it's something to do with Nabble.
There are others pending moderation in pgsql-admin and pgsql-hackers too.

rahul143 wrote:
 I have the created a C-Language function (code is below).  Now, I 
 wonder: How do I handle exceptions, for example if malloc cannot assign 
 the necessary memory?  Do palloc and pfree handle such a case 
 cleanly?  Should I simply use an assert? 
 
 #include postgres.h 
 #include string.h 
 #include stdlib.h 
 #include fmgr.h 
 #include libinn.h 
 
 PG_FUNCTION_INFO_V1(ffiinews_uwildmat); 
 
 /* Wrapper for INN's function uwildmat.  Needs parameters in UTF-8. */ 
 Datum ffiinews_uwildmat(PG_FUNCTION_ARGS) { 
 VarChar *text = PG_GETARG_VARCHAR_P(0); 
 VarChar *pattern = PG_GETARG_VARCHAR_P(1); 
 int text_len = VARSIZE(text)-VARHDRSZ; 
 int pattern_len = VARSIZE(pattern)-VARHDRSZ; 
 char *tmp_text = (char *)malloc(text_len+1); 
 if (tmp_text == NULL) 
 ; /* What now? */ 
 char *tmp_pattern = (char *)malloc(pattern_len+1); 
 if (tmp_pattern == NULL) 
 ; /* What now? */ 
 strncpy(tmp_text, VARDATA(text), text_len); 
 tmp_text[text_len] = '\0'; 
 strncpy(tmp_pattern, VARDATA(pattern), pattern_len); 
 tmp_pattern[pattern_len] = '\0'; 
 bool matches = uwildmat(tmp_text, tmp_pattern); 
 
 
 
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 http://postgresql.1045698.n5.nabble.com/GENERAL-Exception-Handling-in-C-Language-Functions-tp5734656.html
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PostgreSQL Development, 24x7 Support, Training  Services


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Re: [GENERAL] Exception Handling in C-Language Functions?

2005-05-23 Thread greg landrum 

Tom Lane wrote:

Felix E. Klee [EMAIL PROTECTED] writes:

BTW, a more future-proof way of doing what you want:



   VarChar *text = PG_GETARG_VARCHAR_P(0);
   int text_len = VARSIZE(text)-VARHDRSZ;
   char *tmp_text = (char *)malloc(text_len+1);
   if (tmp_text == NULL)
   ; /* What now? */
   strncpy(tmp_text, VARDATA(text), text_len);
   tmp_text[text_len] = '\0';



is to let the varchar output routine do it:

 Datum text_datum = PG_GETARG_DATUM(0);
 char *text;

 text = DatumGetCString(DirectFunctionCall1(varcharout, text_datum));

This avoids assuming that you know the internal representation of
varchar (and if you think that's frozen for eternity, you haven't
been reading the discussions of ramping up our locale support...)


This form of dealing with arguments is interesting to learn about. Is 
there any documentation of this stuff or do I need to dive into the source?


-greg

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Re: [GENERAL] Exception Handling in C-Language Functions?

2005-05-23 Thread Tom Lane 
greg landrum [EMAIL PROTECTED] writes:
 Tom Lane wrote:
 text = DatumGetCString(DirectFunctionCall1(varcharout, text_datum));

 This form of dealing with arguments is interesting to learn about. Is 
 there any documentation of this stuff or do I need to dive into the source?

The original motivation for this notation is discussed in
src/backend/utils/fmgr/README, and there's some basic docs in the
main SGML documentation.  Beyond that, looking at code that does
something close to what you want has always been the best guide ...

regards, tom lane

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[GENERAL] Exception Handling in C-Language Functions?

2005-05-21 Thread Felix E. Klee 
I have the created a C-Language function (code is below).  Now, I
wonder: How do I handle exceptions, for example if malloc cannot assign
the necessary memory?  Do palloc and pfree handle such a case
cleanly?  Should I simply use an assert?

#include postgres.h
#include string.h
#include stdlib.h
#include fmgr.h
#include libinn.h

PG_FUNCTION_INFO_V1(ffiinews_uwildmat);

/* Wrapper for INN's function uwildmat.  Needs parameters in UTF-8. */
Datum ffiinews_uwildmat(PG_FUNCTION_ARGS) {
VarChar *text = PG_GETARG_VARCHAR_P(0);
VarChar *pattern = PG_GETARG_VARCHAR_P(1);
int text_len = VARSIZE(text)-VARHDRSZ;
int pattern_len = VARSIZE(pattern)-VARHDRSZ;
char *tmp_text = (char *)malloc(text_len+1);
if (tmp_text == NULL)
; /* What now? */
char *tmp_pattern = (char *)malloc(pattern_len+1);
if (tmp_pattern == NULL)
; /* What now? */
strncpy(tmp_text, VARDATA(text), text_len);
tmp_text[text_len] = '\0';
strncpy(tmp_pattern, VARDATA(pattern), pattern_len);
tmp_pattern[pattern_len] = '\0';
bool matches = uwildmat(tmp_text, tmp_pattern);
free(tmp_pattern);
free(tmp_text);
PG_RETURN_BOOL(matches);
}

-- 
Felix E. Klee

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Re: [GENERAL] Exception Handling in C-Language Functions?

2005-05-21 Thread Neil Conway 

Felix E. Klee wrote:

I have the created a C-Language function (code is below).  Now, I
wonder: How do I handle exceptions, for example if malloc cannot assign
the necessary memory?  Do palloc and pfree handle such a case
cleanly?


Yes -- they will roll back the current transaction on if there is no 
memory available. You can catch the error via PG_TRY() in 8.0, although 
in the case of OOM there isn't probably a lot your exception handler 
could do...


-Neil

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Re: [GENERAL] Exception Handling in C-Language Functions?

2005-05-21 Thread Felix E. Klee 
At Sat, 21 May 2005 20:13:13 +1000,
Neil Conway wrote:
  Do palloc and pfree handle such a case cleanly?
 
 Yes -- they will roll back the current transaction on if there is no 
 memory available. 

Great.  So I just use those.

 You can catch the error via PG_TRY() in 8.0 [...]

Nice, but we're not deploying 8.0.  However, at the moment, out of
memory exceptions seem to be the only ones that I've to deal with.

-- 
Felix E. Klee

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Re: [GENERAL] Exception Handling in C-Language Functions?

2005-05-21 Thread Tom Lane 
Felix E. Klee [EMAIL PROTECTED] writes:
 I have the created a C-Language function (code is below).  Now, I
 wonder: How do I handle exceptions, for example if malloc cannot assign
 the necessary memory?  Do palloc and pfree handle such a case
 cleanly?  Should I simply use an assert?

As a general rule, never ever use malloc in backend code --- there's way
too much risk of causing a memory leak.  (If your function for some
reason errors out before reaching the free(), that memory is gone.
Lather, rinse, repeat a few million times, as is not unlikely to happen
in a database server, and you've got a big problem.)

Use palloc instead. You don't have to check it for a failure return,
as Neil already noted, and you can be sloppy about remembering to free
the result ... in fact, there's no real reason to free it at all, since
anything palloc gives you inside a function will be short-term memory.
See src/backend/utils/mmgr/README for details.

If you want to report your own errors, use elog/ereport.

BTW, a more future-proof way of doing what you want:

 VarChar *text = PG_GETARG_VARCHAR_P(0);
 int text_len = VARSIZE(text)-VARHDRSZ;
 char *tmp_text = (char *)malloc(text_len+1);
 if (tmp_text == NULL)
 ; /* What now? */
 strncpy(tmp_text, VARDATA(text), text_len);
 tmp_text[text_len] = '\0';

is to let the varchar output routine do it:

 Datum text_datum = PG_GETARG_DATUM(0);
 char *text;

 text = DatumGetCString(DirectFunctionCall1(varcharout, text_datum));

This avoids assuming that you know the internal representation of
varchar (and if you think that's frozen for eternity, you haven't
been reading the discussions of ramping up our locale support...)

regards, tom lane

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Re: [GENERAL] Exception Handling in C-Language Functions?

2005-05-21 Thread Felix E. Klee 
At Sat, 21 May 2005 10:30:47 -0400,
Tom Lane wrote:
 BTW, a more future-proof way of doing what you want:
 
  [...]
 
 is to let the varchar output routine do it:
 
  Datum text_datum = PG_GETARG_DATUM(0);
  char *text;
 
  text = DatumGetCString(DirectFunctionCall1(varcharout, text_datum));
 
 This avoids assuming that you know the internal representation of
 varchar (and if you think that's frozen for eternity, you haven't been
 reading the discussions of ramping up our locale support...)

Thanks for all those hints!  I've now adapted my code as you recommended
and it works fine, although I'm not certain what DirectFunctionCall1 and
DatumGetCString actually do (it seems that the only documentation of
these functions is in the source code, and I'm too lazy to sift through
it at the moment).

-- 
Felix E. Klee

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