use break conditions

(gdb) break frik.c:13 thread 28 if bartab > lim 

see Debugging with GDB

use break conditions

(gdb) break frik.c:13 thread 28 if bartab > lim 

see Debugging with GDB

Edit:

(gdb) break <thread_function_entry_point> thread 2 (gdb) break <thread_function_entry_point> thread 1 (gdb) thread 1 (gdb) continue (gdb) ... thread 1 finishes (gdb) thread 2 (gdb) continue 

You can put these commands inside a .gdbrc file.