6.2. The trace approach
Many times the code returned by the invoked function is not sufficient to understand what's happening: libjf is developed using an "exception oriented programming style" I named "sequential programming" some times ago. The idea at the root of this programming style is: "nidification is a bad thing, try to write code with as small nidification as possible".
To see the "stack trace" of the called function, you must do two things:
activate "debug" feature when building libjf:
./configure --enable-debug make make check sudo make install
set environment variable JF_TRACE_MASK before start your program:
export JF_TRACE_MASK=0xffffffff
tiian@linux:~/tutorial> ./jf_strerror
jf_file_close
jf_file_close/excp=0/ret_cod=-9/errno=0
libjf error: ERROR: object is corrupted (-9)
When running a complex application, mask "0xffffffff" will produce a lot of messages, too many messages. To determine the value you need, take a look to file jf/jf_trace.h: you can activate/deactivate the trace feature at module level and get only the messages you need. This is an excerpt of jf/jf_trace.h:
[...]
/**
* trace module for library module "jf_cache_file"
*/
#define JF_TRACE_MOD_LIB_CACHE_FILE 0x00000001
/**
* trace module for library module "jf_crash_simul"
*/
#define JF_TRACE_MOD_LIB_CRASH_SIMUL 0x00000002
/**
* trace module for library module "jf_file"
*/
#define JF_TRACE_MOD_LIB_FILE 0x00000004
/**
* trace module for library module "jf_journal_file_tab"
*/
#define JF_TRACE_MOD_LIB_JOURNAL_FILE_TAB 0x00000008
/**
* trace module for library module "jf_utils"
*/
#define JF_TRACE_MOD_LIB_UTILS 0x00000010
/**
* trace module for library module "jf_journal"
*/
#define JF_TRACE_MOD_LIB_JOURNAL 0x00000020
[...]
if you need only messages printed by "jf_journal" and
"jf_file" modules, you have to set
JF_TRACE_MASK to "0x00000024".
Any combination of values is allowed.
 | Don't use a library built with "debug" feature in production environment: performances may degrade even if JF_TRACE_MASK is not set. |
6.2.1. How can I guess if libjf was compiled with debug feature?
If you don't remember how libjf was compiled or someone but you installed it, you can retrieve configuration features with this command:
tiian@linux:~> strings /opt/libjf/lib/libjf | grep 'feature/'
feature/timer = yes
feature/debug = yes
feature/crash_simul = no
feature/cache_stress = no
feature/extra_check = no
pay attention the actual name of the library is system dependent:
it could be libjf.a,
libjf.so, libjf.sl, etc...