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 locspec thread thread-id
break locspec thread thread-id if …
locspec specifies a code location or locations in your program. See Location Specifications, for details.
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
explicitly asks for the thread list with the
A breakpoint can’t be both thread-specific and inferior-specific
(see Inferior-Specific Breakpoints), or task-specific (see Ada Tasks); using more than one of the
task keywords when creating a breakpoint will give an error.