    % scons -Q --taskmastertrace=- prog

    Taskmaster: Looking for a node to evaluate
    Taskmaster:     Considering node <no_state   0   'prog'> and its children:
    Taskmaster:        <no_state   0   'prog.o'>
    Taskmaster:      adjusted ref count: <pending    1   'prog'>, child 'prog.o'
    Taskmaster:     Considering node <no_state   0   'prog.o'> and its children:
    Taskmaster:        <no_state   0   'prog.c'>
    Taskmaster:        <no_state   0   'inc.h'>
    Taskmaster:      adjusted ref count: <pending    1   'prog.o'>, child 'prog.c'
    Taskmaster:      adjusted ref count: <pending    2   'prog.o'>, child 'inc.h'
    Taskmaster:     Considering node <no_state   0   'prog.c'> and its children:
    Taskmaster: Evaluating <pending    0   'prog.c'>

    Task.make_ready_current(): node <pending    0   'prog.c'>
    Task.prepare():      node <up_to_date 0   'prog.c'>
    Task.executed_with_callbacks(): node <up_to_date 0   'prog.c'>
    Task.postprocess():  node <up_to_date 0   'prog.c'>
    Task.postprocess():  removing <up_to_date 0   'prog.c'>
    Task.postprocess():  adjusted parent ref count <pending    1   'prog.o'>

    Taskmaster: Looking for a node to evaluate
    Taskmaster:     Considering node <no_state   0   'inc.h'> and its children:
    Taskmaster: Evaluating <pending    0   'inc.h'>

    Task.make_ready_current(): node <pending    0   'inc.h'>
    Task.prepare():      node <up_to_date 0   'inc.h'>
    Task.executed_with_callbacks(): node <up_to_date 0   'inc.h'>
    Task.postprocess():  node <up_to_date 0   'inc.h'>
    Task.postprocess():  removing <up_to_date 0   'inc.h'>
    Task.postprocess():  adjusted parent ref count <pending    0   'prog.o'>

    Taskmaster: Looking for a node to evaluate
    Taskmaster:     Considering node <pending    0   'prog.o'> and its children:
    Taskmaster:        <up_to_date 0   'prog.c'>
    Taskmaster:        <up_to_date 0   'inc.h'>
    Taskmaster: Evaluating <pending    0   'prog.o'>

    Task.make_ready_current(): node <pending    0   'prog.o'>
    Task.prepare():      node <executing  0   'prog.o'>
    Task.execute():      node <executing  0   'prog.o'>
    cc -o prog.o -c -I. prog.c
    Task.executed_with_callbacks(): node <executing  0   'prog.o'>
    Task.postprocess():  node <executed   0   'prog.o'>
    Task.postprocess():  removing <executed   0   'prog.o'>
    Task.postprocess():  adjusted parent ref count <pending    0   'prog'>

    Taskmaster: Looking for a node to evaluate
    Taskmaster:     Considering node <pending    0   'prog'> and its children:
    Taskmaster:        <executed   0   'prog.o'>
    Taskmaster: Evaluating <pending    0   'prog'>

    Task.make_ready_current(): node <pending    0   'prog'>
    Task.prepare():      node <executing  0   'prog'>
    Task.execute():      node <executing  0   'prog'>
    cc -o prog prog.o
    Task.executed_with_callbacks(): node <executing  0   'prog'>
    Task.postprocess():  node <executed   0   'prog'>

    Taskmaster: Looking for a node to evaluate
    Taskmaster: No candidate anymore.