10.5 Futures Visualizer

Parallelism with Futures in The Racket Guide introduces the future visualizer.

(require future-visualizer)

The futures visualizer is a graphical profiling tool for parallel programs written using future. The tool shows a timeline of a program’s execution including all future-related events, as well as the overall amount of processor utilization at any point during the program’s lifetime.

A typical program using profiling might look like the following:

(require racket/future

future-visualizer)

(visualize-futures

(let ([f (future (lambda () ...))])

...

(touch f)))

The preceding program is equivalent to:

(require racket/future

future-visualizer/trace

future-visualizer)

(start-future-tracing!)

(let ([f (future (lambda () ...))])

...

(touch f))

(stop-future-tracing!)

(show-visualizer)

10.5.1 Execution Timeline

The execution timeline, shown in the top left-hand corner of the profiler window, displays a history of the program and all events associated with its futures, with OS-level threads or processes organized along the y-axis and time increasing along the x-axis. A coloring convention is used to distinguish between different types of events (see Future Performance Logging for a full description of these event types):

• Blue dot: 'create

• Green bar: 'start-work, 'start-0-work

• Orange dot: 'sync

• Red dot: 'block, 'touch

• White dot: 'result, 'end-work

• Green dot: 'touch-pause, 'touch-resume

Mousing over any event connects it via purple lines to the sequence of events for its future. Additionally, orange dotted lines with arrowheads may be shown to indicate operations performed from one future to another (e.g. 'create or 'touch actions). To view details about two events simultaneously, a selection can be tacked by clicking the mouse.

The timeline displays vertical lines at 100-microsecond intervals. Note that though the time interval is fixed, the pixel distance between lines varies based on the event density for any given time range to prevent overlapping event circles.

10.5.2 Future Creation Tree

The creation tree shows a tree with a single node per future created by the program. This display can be particularly useful for programs which spawn futures in nested fashion (futures within futures). For any given future node, the children of that node represent futures which were created by that future (within the scope of its thunk). For all programs, the root of the tree is a special node representing the main computation thread (the runtime thread), and is denoted RTT.