5.5.4 Thread-Specific Breakpoints

When your program has multiple threads (see Debugging Programs with Multiple Threads), you can choose whether to set breakpoints on all threads, or on a particular thread.

break linespec thread threadno

break linespec thread threadno if ...

linespec specifies source lines; there are several ways of writing them (see Specify Location), but the effect is always to specify some source line.

Use the qualifier ‘thread threadno’ with a breakpoint command to specify that you only want gdb to stop the program when a particular thread reaches this breakpoint. threadno is one of the numeric thread identifiers assigned by gdb, shown in the first column of the ‘info threads’ display.

If you do not specify ‘thread threadno’ when you set a breakpoint, the breakpoint applies to all threads of your program.

You can use the thread qualifier on conditional breakpoints as well; in this case, place ‘thread threadno’ before or after the breakpoint condition, like this:

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

Thread-specific breakpoints are automatically deleted when gdb detects the corresponding thread is no longer in the thread list. For example:

     (gdb) c
     Thread-specific breakpoint 3 deleted - thread 28 no longer in the thread list.

There are several ways for a thread to disappear, such as a regular thread exit, but also when you detach from the process with the detach command (see Debugging an Already-running Process), or if gdb loses the remote connection (see Remote Debugging), etc. Note that with some targets, gdb is only able to detect a thread has exited when the user explictly asks for the thread list with the info threads command.