Ada Tasks (Debugging with GDB)

15.4.10.7 Extensions for Ada Tasks

Support for Ada tasks is analogous to that for threads (see Threads). GDB provides the following task-related commands:

info tasks

This command shows a list of current Ada tasks, as in the following example:

(gdb) info tasks
  ID       TID P-ID Pri State                 Name
   1   8088000   0   15 Child Activation Wait main_task
   2   80a4000   1   15 Accept Statement      b
   3   809a800   1   15 Child Activation Wait a
*  4   80ae800   3   15 Runnable              c

In this listing, the asterisk before the last task indicates it to be the task currently being inspected.

ID: Represents GDB’s internal task number.
TID: The Ada task ID.
P-ID: The parent’s task ID (GDB’s internal task number).
Pri: The base priority of the task.
State: Current state of the task.

Unactivated The task has been created but has not been activated. It cannot be executing. Runnable The task is not blocked for any reason known to Ada. (It may be waiting for a mutex, though.) It is conceptually "executing" in normal mode. Terminated The task is terminated, in the sense of ARM 9.3 (5). Any dependents that were waiting on terminate alternatives have been awakened and have terminated themselves. Child Activation Wait The task is waiting for created tasks to complete activation. Accept Statement The task is waiting on an accept or selective wait statement. Waiting on entry call The task is waiting on an entry call. Async Select Wait The task is waiting to start the abortable part of an asynchronous select statement. Delay Sleep The task is waiting on a select statement with only a delay alternative open. Child Termination Wait The task is sleeping having completed a master within itself, and is waiting for the tasks dependent on that master to become terminated or waiting on a terminate Phase. Wait Child in Term Alt The task is sleeping waiting for tasks on terminate alternatives to finish terminating. Accepting RV with taskno The task is accepting a rendez-vous with the task taskno.

Name: Name of the task in the program.

info task taskno

This command shows detailed informations on the specified task, as in the following example:

(gdb) info tasks
  ID       TID P-ID Pri State                  Name
   1   8077880    0  15 Child Activation Wait  main_task
*  2   807c468    1  15 Runnable               task_1
(gdb) info task 2
Ada Task: 0x807c468
Name: "task_1"
Thread: 0
LWP: 0x1fac
Parent: 1 ("main_task")
Base Priority: 15
State: Runnable

task

This command prints the ID and name of the current task.

(gdb) info tasks
  ID       TID P-ID Pri State                  Name
   1   8077870    0  15 Child Activation Wait  main_task
*  2   807c458    1  15 Runnable               some_task
(gdb) task
[Current task is 2 "some_task"]

task taskno

This command is like the thread thread-id command (see Threads). It switches the context of debugging from the current task to the given task.

(gdb) info tasks
  ID       TID P-ID Pri State                  Name
   1   8077870    0  15 Child Activation Wait  main_task
*  2   807c458    1  15 Runnable               some_task
(gdb) task 1
[Switching to task 1 "main_task"]
#0  0x8067726 in pthread_cond_wait ()
(gdb) bt
#0  0x8067726 in pthread_cond_wait ()
#1  0x8056714 in system.os_interface.pthread_cond_wait ()
#2  0x805cb63 in system.task_primitives.operations.sleep ()
#3  0x806153e in system.tasking.stages.activate_tasks ()
#4  0x804aacc in un () at un.adb:5

break location task taskno

break location task taskno if …

These commands are like the break … thread … command (see Thread Stops). The location argument specifies source lines, as described in Specify Location.

Use the qualifier ‘task taskno’ with a breakpoint command to specify that you only want GDB to stop the program when a particular Ada task reaches this breakpoint. The taskno is one of the numeric task identifiers assigned by GDB, shown in the first column of the ‘info tasks’ display.

If you do not specify ‘task taskno’ when you set a breakpoint, the breakpoint applies to all tasks of your program.

You can use the task qualifier on conditional breakpoints as well; in this case, place ‘task taskno’ before the breakpoint condition (before the if).

For example,

(gdb) info tasks
  ID       TID P-ID Pri State                 Name
   1 140022020   0   15 Child Activation Wait main_task
   2 140045060   1   15 Accept/Select Wait    t2
   3 140044840   1   15 Runnable              t1
*  4 140056040   1   15 Runnable              t3
(gdb) b 15 task 2
Breakpoint 5 at 0x120044cb0: file test_task_debug.adb, line 15.
(gdb) cont
Continuing.
task # 1 running
task # 2 running

Breakpoint 5, test_task_debug () at test_task_debug.adb:15
15               flush;
(gdb) info tasks
  ID       TID P-ID Pri State                 Name
   1 140022020   0   15 Child Activation Wait main_task
*  2 140045060   1   15 Runnable              t2
   3 140044840   1   15 Runnable              t1
   4 140056040   1   15 Delay Sleep           t3