Looking at the Threads. Simple Debugging

In a multithreaded application, you can obtain information about the thread that stopped or about all the threads, and you can then change the context to look more closely at a different thread. Note that a right bracket (>) marks the current thread. And the asterisk (*) marks the thread with return status.

DBX Mode

(idb) thread

  Thread Name                      State           Substate    Policy       Pri

  ------ ------------------------- --------------- ----------- ------------ ---

>*     1 default thread            running VP 3                SCHED_OTHER  19

(idb) show thread

  Thread Name                      State           Substate    Policy       Pri

  ------ ------------------------- --------------- ----------- ------------ ---

>*     1 default thread            running VP 3                SCHED_OTHER  19

      -1 manager thread            blk SCS                     SCHED_RR     19

      -2 null thread for slot 0    running VP 1                null thread  -1

      -3 null thread for slot 1    ready VP 3                  null thread  -1

      -4 null thread for slot 2    new             new         null thread  -1

      -5 null thread for slot 3    new             new         null thread  -1

       2 threads(0x140000798)      blocked         cond 3      SCHED_OTHER  19

       3 threads+8(0x1400007a0)    blocked         cond 3      SCHED_OTHER  19

       4 threads+16(0x1400007a8)   blocked         cond 3      SCHED_OTHER  19

       5 threads+24(0x1400007b0)   blocked         cond 3      SCHED_OTHER  19

       6 threads+32(0x1400007b8)   blocked         cond 3      SCHED_OTHER  19

You can select any thread to be the focus of commands that show things. For example:

(idb) thread 2

  Thread Name                      State           Substate    Policy       Pri

  ------ ------------------------- --------------- ----------- ------------ ---

>      2 threads(0x140000798)      blocked         cond 3      SCHED_OTHER  19

GDB Mode

Within the GDB mode, you can have a look at a particular thread by specifying the internal debugger thread number. The asterisk (*) marks the current thread. Or you can observe all threads while your program is running:

(idb) thread

   ID           State

>* 8            stopped

(idb) show thread

   ID           State

   1            stopped

   2            stopped

   3            stopped

   4            stopped

   5            stopped

   6            stopped

   7            stopped

>* 8            stopped

This command provides the following information about known threads:

• Number: Number of a thread from the debugger point of view. This number is not used for numbering again if a thread dies.
• Thread TID: Thread identifier. TID is an identifier (unique) assigned to each thread inside the thread library.

• LWP PID: Light weight process identifier (unique) assigned by the Linux kernel to each process in the system. Architecturally, LinuxThreads has a PID for each thread in a multithreaded application.

• Location: Location where the thread stopped. Its output is very similar to the backtrace location field.

You can select any thread to be the focus of commands that show things. For example:

(idb) thread 2

   ID           State

>  2            stopped