Support for task dependency visualization

[rexdex]

Typically in some form of task-graph system or similar arrangement starting one task depends on completion of other(s). Being able to visualize those dependencies in the profiler would be a very useful feature.

Concept:

API would be rather simple:

id = EASY_DEPENDENCY_SOURCE() - creates a "source" point of dependency on the current thread, returns opaque ID to pass to the other function. This is the start of the arrow. Time should be remembered exactly, the source can be assumed to be in the current block.

EASY_DEPENDENCY_TARGET(id, color) - creates a "target" point of dependency (arrow's head). Time should be remembered exactly and it can be assumed that the target exists in the current block.

Such API would allow to integrate dependency tracking in multiple scenarios:

• Task Graph dependencies
• sequence multiple IO operations
• CPU to GPU timing mapping (with some extra massaging)
• places where fiber is yielded and resumed
• events/semaphores and places where events are released
• many more