[SOLVED] Segmentation fault in client on 2nd cursor mysql_stmt_fetch
Posted by: Michael Soltis
Date: January 18, 2012 09:52PM

I'm creating a prepared statement involving a query with 1 (bind) parameter and 1 (bind) result (and returning 1 row). The statement has its STMT_ATTR_CURSOR_TYPE set to CURSOR_TYPE_READ_ONLY and prefetches 1 row.

The statement 'stmt1' executes fine and I can fetch the single result. However, if I create a subsequent statement 'stmt2' with different data structures than stmt1, things go wrong.

If run mysql_stmt_close(stmt1) before running mysql_stmt_fetch(stmt2), then mysql_stmt_fetch(stmt2) fails and mysql reports "Prepared statement contains no metadata". If I don't run mysql_stmt_close(stmt1) before running mysql_stmt_fetch(stmt2) then the program produces a segmentation fault on mysql_stmt_fetch(stmt2).

Both statements are created (mysql_stmt_init) from the same database connection.

From what I've read, it seems that I should be able to have more than 1 prepared statement created from a single connection as long STMT_ATTR_CURSOR_TYPE is CURSOR_TYPE_READ_ONLY for both statements. While debugging the statements, stmt1 has stmt_id = 1 and stmt2 has stmt_id = 2. Both are bound to different MYSQL_BIND[] instances and use different parameters and results. In effect, both statements are separate other than having being initialized (mysql_stmt_init) from the same database connection.

stmt1 before calling fetch:

mem_root = {
free = 0x6552d0,
used = 0x0,
pre_alloc = 0x6552d0,
min_malloc = 32,
block_size = 2016,
block_num = 4,
first_block_usage = 0,
error_handler = 0
},
list = {
prev = 0x0,
next = 0x0,
data = 0x654f50
},
mysql = 0x63b200,
params = 0x6553a0,
bind = 0x655410,
fields = 0x6552e0,
result = {
data = 0x0,
embedded_info = 0x0,
alloc = {
free = 0x655af0,
used = 0x0,
pre_alloc = 0x655af0,
min_malloc = 24,
block_size = 4064,
block_num = 4,
first_block_usage = 0,
error_handler = 0
},
rows = 0,
fields = 0,
extension = 0x0
},
data_cursor = 0x0,
read_row_func = 0x7ffff7920700,
affected_rows = 18446744073709551615,
insert_id = 0,
stmt_id = 1,
flags = 1,
prefetch_rows = 1,
server_status = 66,
last_errno = 0,
param_count = 1,
field_count = 1,
state = MYSQL_STMT_EXECUTE_DONE,
last_error = '\000' <repeats 511 times>,
sqlstate = "00000",
send_types_to_server = 0 '\000',
bind_param_done = 1 '\001',
bind_result_done = 3 '\003',
unbuffered_fetch_cancelled = 0 '\000',
update_max_length = 0 '\000',
extension = 0x655290
}

stmt1 after calling fetch:

mem_root = {
free = 0x6552d0,
used = 0x0,
pre_alloc = 0x6552d0,
min_malloc = 32,
block_size = 2016,
block_num = 4,
first_block_usage = 0,
error_handler = 0
},
list = {
prev = 0x656db8,
next = 0x0,
data = 0x654f50
},
mysql = 0x63b200,
params = 0x6553a0,
bind = 0x655410,
fields = 0x6552e0,
result = {
data = 0x0,
embedded_info = 0x0,
alloc = {
free = 0x655af0,
used = 0x0,
pre_alloc = 0x655af0,
min_malloc = 24,
block_size = 4064,
block_num = 4,
first_block_usage = 0,
error_handler = 0
},
rows = 0,
fields = 0,
extension = 0x0
},
data_cursor = 0x0,
read_row_func = 0x7ffff791cec0,
affected_rows = 18446744073709551615,
insert_id = 0,
stmt_id = 1,
flags = 1,
prefetch_rows = 1,
server_status = 130,
last_errno = 0,
param_count = 1,
field_count = 1,
state = MYSQL_STMT_PREPARE_DONE,
last_error = '\000' <repeats 511 times>,
sqlstate = "00000",
send_types_to_server = 0 '\000',
bind_param_done = 1 '\001',
bind_result_done = 3 '\003',
unbuffered_fetch_cancelled = 0 '\000',
update_max_length = 0 '\000',
extension = 0x655290
}

stmt2 before calling fetch having called mysql_stmt_close(stmt1):

mem_root = {
free = 0x657100,
used = 0x0,
pre_alloc = 0x657100,
min_malloc = 32,
block_size = 2016,
block_num = 4,
first_block_usage = 0,
error_handler = 0
},
list = {
prev = 0x0,
next = 0x654f88,
data = 0x656d80
},
mysql = 0x63b200,
params = 0x6571e0,
bind = 0x657250,
fields = 0x657110,
result = {
data = 0x0,
embedded_info = 0x0,
alloc = {
free = 0x657920,
used = 0x0,
pre_alloc = 0x657920,
min_malloc = 24,
block_size = 4064,
block_num = 4,
first_block_usage = 0,
error_handler = 0
},
rows = 0,
fields = 0,
extension = 0x0
},
data_cursor = 0x0,
read_row_func = 0x7ffff7920700,
affected_rows = 18446744073709551615,
insert_id = 0,
stmt_id = 2,
flags = 1,
prefetch_rows = 1,
server_status = 66,
last_errno = 0,
param_count = 1,
field_count = 1,
state = MYSQL_STMT_EXECUTE_DONE,
last_error = '\000' <repeats 511 times>,
sqlstate = "00000",
send_types_to_server = 0 '\000',
bind_param_done = 1 '\001',
bind_result_done = 3 '\003',
unbuffered_fetch_cancelled = 0 '\000',
update_max_length = 0 '\000',
extension = 0x6570c0
}

I'm running mysql 5.5.18 on x86_64.

Thanks.



Edited 1 time(s). Last edit at 01/23/2012 10:46PM by Michael Soltis.

Options: ReplyQuote


Subject
Views
Written By
Posted
[SOLVED] Segmentation fault in client on 2nd cursor mysql_stmt_fetch
2245
January 18, 2012 09:52PM


Sorry, you can't reply to this topic. It has been closed.

Content reproduced on this site is the property of the respective copyright holders. It is not reviewed in advance by Oracle and does not necessarily represent the opinion of Oracle or any other party.