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 or Select Term

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.

Asynchronous Hold

The task has been held by Ada.Asynchronous_Task_Control.Hold_Task.

Activating

The task has been created and is being made runnable.

Selective Wait

The task is waiting in a selective wait statement.

Accepting RV with taskno

The task is accepting a rendez-vous with the task taskno.

Waiting on RV with taskno

The task is waiting for a rendez-vous with the task taskno.

Name

Name of the task in the program.

info task taskno

This command shows detailed information 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

task apply [task-id-list | all] [flag]… command

The task apply command is the Ada tasking analogue of thread apply (see Threads). It allows you to apply the named command to one or more tasks. Specify the tasks that you want affected using a list of task IDs, or specify all to apply to all tasks.

The flag arguments control what output to produce and how to handle errors raised when applying command to a task. flag must start with a - directly followed by one letter in qcs. If several flags are provided, they must be given individually, such as -c -q.

By default, GDB displays some task information before the output produced by command, and an error raised during the execution of a command will abort task apply. The following flags can be used to fine-tune this behavior:

-c

The flag -c, which stands for ‘continue’, causes any errors in command to be displayed, and the execution of task apply then continues.

-s

The flag -s, which stands for ‘silent’, causes any errors or empty output produced by a command to be silently ignored. That is, the execution continues, but the task information and errors are not printed.

-q

The flag -q (‘quiet’) disables printing the task information.

Flags -c and -s cannot be used together.

break locspec task taskno

break locspec task taskno if …

These commands are like the break … thread … command (see Thread Stops). See Location Specifications, for the various forms of locspec.

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