MySQL thread-unsafe library gets linked? wut?
lazarus / 16-Databases

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hinst · 2013-11-22 20:06

I run into some problems in my multithreaded application which uses
fcl-db.
While searching for answers, here is what I found: MySQL has two
client libraries on linux:
libmysqlclient.so which is thread-unsafelibmysqlclient_r.so which is
thread-safe
Then I performed a full-text search in Lazarus directory (which
contains FreePascal sources as well)... I searched for
"libmysqlclient" string is present in some source files, but
libmysqlclient_r is not...
So does that mean that fcl-db only links thread-unsafe mysql client
library? (whether dynamically or statically is irrelevant at this
point. In case my application uses thread-unsafe library, the problems
I ran into are most likely are caused by the usage of thread-unsafe
library)

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marcov · 2013-11-22 20:15

Override the library name (see the mysql unit for how), and test.

This kind of rough speculation isn't beneficial to anyone.

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hinst · 2013-11-22 21:06

I just checked it, but in another way
Because to make changes in RTL units such as mysql, I have to
recompile the FPC compiler's RTL, and it won't get recompiled
automatically when I recompile my applicationIt turns out that it uses
"unsafe" library.
Here is how I checked: launched my application, then obtained its
process id
Code: [Select]$ pidof GTIWebServer
10792
Then:
Code: [Select]$lsof -P -T -p 10792
...
GTIWebSer 10792 hinst  mem    REG              252,2  1030512  265934
/lib/x86_64-linux-gnu/libm-2.15.so
GTIWebSer 10792 hinst  mem    REG              252,2    92720  262373
/lib/x86_64-linux-gnu/libz.so.1.2.3.4
GTIWebSer 10792 hinst  mem    REG              252,2  3412232 2366616
/usr/lib/x86_64-linux-gnu/libmysqlclient.so.18.0.0
GTIWebSer 10792 hinst  mem    REG              252,2  1815224  265923
/lib/x86_64-linux-gnu/libc-2.15.so
... other libraries below
It also turns out that FPC loads mysql library dynamically by default
(because this command lists only dynamic libraries)
One last thing: I checked whether an equal .so file exists but with
_r:
/usr/lib/x86_64-linux-gnu/libmysqlclient_r.so.18
and it does exist indeed. So everything points to the fact that
thread-unsafe MySQL library is being used indeed