Thread-Specific Breakpoints (Debugging with GDB)

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 location thread thread-id

break location thread thread-id if …

location 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 thread-id’ with a breakpoint command to specify that you only want GDB to stop the program when a particular thread reaches this breakpoint. The thread-id specifier is one of the thread identifiers assigned by GDB, shown in the first column of the ‘info threads’ display.

If you do not specify ‘thread thread-id’ 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 thread-id’ 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.