2.4. Hello world II


Every saga needs at least a second episode.

What happens if data are not committed to a journaled file? To discover the core of libjf transactionality it's sufficient to remove jf_file_commit statement as in hello_world2.c example:

Example 2-2. hello_world2.c

     1	#include <jf_file.h>
     2	int main()
     3	{
     4	        int rc;
     5	        jf_file_t jf;
     6	        size_t write;
     7	        rc = jf_file_open(&jf, NULL, "jf_tut_foo", "w", NULL);
     8	        if (JF_RC_OK != rc)
     9	                return 1;
    10	        rc = jf_file_printf(&jf, &write, "%s", "Hello world!\n");
    11	        if (JF_RC_OK != rc)
    12	                return 1;
    13	        rc = jf_file_close(&jf);
    14	        if (JF_RC_OK != rc)
    15	                return 1;
    16	        printf("Hello world II program is OK!\n");
    17	        return 0;
    18	}
Compile hello_world2.c with command:
libtool --mode=link gcc -Wall -I/opt/libjf/include -L/opt/libjf/lib -ljf \
        -o hello_world2 hello_world2.c
remove temporary files wrote by hello_world:
tiian@linux:~/tutorial> rm -f jf_tut_foo*
and run hello_world2 program:
tiian@linux:~/tutorial> ./hello_world2
Hello world II program is OK!
Take a look to files produced by hello_world2 execution:
tiian@linux:~/tutorial> ls -la jf_tut_foo*
-rw-r--r--  1 tiian users    0 2005-08-11 11:05 jf_tut_foo
-rw-r--r--  1 tiian users 8278 2005-08-11 11:05 jf_tut_foo.jf
jf_tut_foo is now an empty file because data was not committed before calling jf_file_close (this behavior is named "implicit rollback"); just for the sake of curiosity, inspect the associated journal file:
tiian@linux:~/tutorial> jf_report -dt -j jf_tut_foo.jf
<?xml version="1.0" encoding="UTF-8"?>
  <header magic_number='0x41524153' version='1' file_id_mask='0x8' 
      file_id_mask_shift='3' size_mask='0xfffffff0' size_mask_shift='4' 
      file_size='4194304' file_num='3' rotation_threshold='0.800' 
      ctrl_recs='36' journal_recs='8278' />
  <journaled_file_table max_files='2' number_of_files='2' 
    <file id='0' name='jf_tut_foo.jf' last_pos='8278' last_size='0' 
        status='0' last_uc_pos='0' last_uc_size='8278' stream='0x804b008' />
    <file id='1' name='jf_tut_foo' last_pos='0' last_size='0' status='0' 
        last_uc_pos='0' last_uc_size='0' stream='(nil)' />
no records have been written.