When you are working with two or more journaled files, sometimes you need to close a "partial transaction" before the global transaction has completed: this happens when you want to save the fact you tried the transaction and a rollback would erase this information. The following example will show this behavior.
Example 3-3. two_files_crash2.c
1 #include <jf_file.h>
2 int main()
3 {
4 int rc;
5 size_t write;
6 jf_journal_t j;
7 jf_file_t jf1, jf2;
8 struct jf_journal_opts_s jopts;
9 struct jf_file_open_opts_s fopts;
10 const char *file1_data1 = "First string for first file\n";
11 const char *file1_data2 = "Second string for first file\n";
12 const char *file2_data1 = "First string for second file\n";
13 const char *file2_data2 = "Second string for second file\n";
14 int x, y;
15 jf_set_default_journal_opts(&jopts);
16 jopts.flags |= JF_JOURNAL_PROP_OPEN_O_CREAT |
17 JF_JOURNAL_PROP_OPEN_O_EXCL;
18 rc = jf_journal_open(&j, "jf_tut_foo-journal", 2, &jopts);
19 if (JF_RC_OK != rc) {
20 printf("%d/%s\n", rc, jf_strerror(rc));
21 return 1;
22 }
23 jf_set_default_file_open_opts(&fopts);
24 fopts.join_the_journal = TRUE;
25 rc = jf_file_open(&jf1, &j, "jf_tut_foo-data1", "w", &fopts);
26 if (JF_RC_OK != rc) {
27 printf("%d/%s\n", rc, jf_strerror(rc));
28 return 1;
29 }
30 rc = jf_file_open(&jf2, &j, "jf_tut_foo-data2", "w", &fopts);
31 if (JF_RC_OK != rc) {
32 printf("%d/%s\n", rc, jf_strerror(rc));
33 return 1;
34 }
35 rc = jf_file_write(&jf1, file1_data1, strlen(file1_data1),
36 &write);
37 if (JF_RC_OK != rc) {
38 printf("%d/%s\n", rc, jf_strerror(rc));
39 return 1;
40 }
41 rc = jf_file_write(&jf2, file2_data1, strlen(file2_data1),
42 &write);
43 if (JF_RC_OK != rc) {
44 printf("%d/%s\n", rc, jf_strerror(rc));
45 return 1;
46 }
47 rc = jf_file_commit(&jf2);
48 if (JF_RC_OK != rc) {
49 printf("%d/%s\n", rc, jf_strerror(rc));
50 return 1;
51 }
52 rc = jf_file_write(&jf1, file1_data2, strlen(file1_data2),
53 &write);
54 if (JF_RC_OK != rc) {
55 printf("%d/%s\n", rc, jf_strerror(rc));
56 return 1;
57 }
58 rc = jf_file_write(&jf2, file2_data2, strlen(file2_data2),
59 &write);
60 if (JF_RC_OK != rc) {
61 printf("%d/%s\n", rc, jf_strerror(rc));
62 return 1;
63 }
64 /* a fool crash simulation */
65 x = 0; y = 5;
66 while (TRUE)
67 x += 5 / y--;
68 printf("This should not print x = %d\n", x);
69 rc = jf_file_close(&jf1);
70 if (JF_RC_OK != rc) {
71 printf("%d/%s\n", rc, jf_strerror(rc));
72 return 1;
73 }
74 rc = jf_file_close(&jf2);
75 if (JF_RC_OK != rc) {
76 printf("%d/%s\n", rc, jf_strerror(rc));
77 return 1;
78 }
79 rc = jf_journal_close(&j);
80 if (JF_RC_OK != rc) {
81 printf("%d/%s\n", rc, jf_strerror(rc));
82 return 1;
83 }
84 printf("two_files_crash II program ended OK!\n");
85 return 0;
86 }
At row 47, we changed
jf_journal_commit(&j) with
jf_file_commit(&jf2): instead
of committing
the whole "unit of work", we decided to commit only the
changes operated against jf2.
The source two_files_crash2.c can be compiled with this command:
libtool --mode=link gcc -Wall -I/opt/libjf/include -L/opt/libjf/lib -ljf \
-o two_files_crash2 two_files_crash2.c
execute it after you have deleted journal and journaled files created by
two_files_crash:
tiian@linux:~/tutorial> rm jf_tut_foo-*
tiian@linux:~/tutorial> ./two_files_crash2
Floating point exception
take a look to files produced by two_files_crash2:
tiian@linux:~/tutorial> ls -la jf_tut_foo-*
-rw-r--r-- 1 tiian users 0 2005-08-12 22:37 jf_tut_foo-data1
-rw-r--r-- 1 tiian users 29 2005-08-12 22:37 jf_tut_foo-data2
-rw-r--r-- 1 tiian users 16561 2005-08-12 22:37 jf_tut_foo-journal
tiian@linux:~/tutorial> cat jf_tut_foo-data2
First string for second file
first journaled file is empty because no data has been committed to it,
second journaled file contains the first string because a partial commit
has been performed.
Can libjf commit/rollback a random set of journaled files? At the time of this writing, libjf can commit/rollback only:
all the journaled files associated to a journal
a specific journaled file