Given the following requirements
- A task x produces a header used in c/c++ compilations
- The c/c++ task depends on the production of that header
- That c task must be executed whenever the header actually changes
- The header may or may not be updated, but the header production task must run each time
The following example demonstrates how to create a task type fulfilling the requirements, and how to use it.
import Task, Constants, Build, Utils
cls = Task.simple_task_type('svnversion', 'date > ${TGT}', color='BLUE') 
cls.runnable_status = lambda self: Constants.RUN_ME 
cls.before = 'cxx' 
old_post_run = cls.post_run
def post_run(self):
old_post_run(self)
Build.bld.node_sigs[self.env.variant()][self.outputs[0].id] = \
Utils.h_file(self.outputs[0].abspath(self.env))
cls.post_run = post_run 
def build(bld):
tsk = cls(bld.env.copy()) 
tsk.inputs = []
tsk.outputs = [bld.path.find_or_declare('foo.h')] 
def set_options(opt):
pass
def configure(conf):
pass
Create a new task type, in this example, we pretend it runs a command to retrieve the svn version and stores it in a header. | |
Replace runnable_status by a new method which indicates the task must be run each time | |
Indicate that the task must always be run before c++ ones | |
By default, the task signature is assigned to the node information. In our case the task signature is always the same, and we need a way to indicate to dependent tasks that something has changed. The solution is to compute a hash of the file produced, and to assign it to the node information. | |
Demonstrate the manual creation of the task | |
The task outputs are Node instances, but there are no inputs. |