Overview/Examples/6. Staying inside a time budget

worked example 6 of 6

Staying inside a time budget

A Progress callback returning false cancels cleanly, leaving a valid intermediate mesh, so a long operation can be bounded by wall-clock time rather than by guesswork.

Example 6 of six - the program sits on the examples page, and this page takes it from the running end: the console it produces, the Status values that end it early, and the options worth changing.

What it prints

stage quadrics   8%
stage collapse  61%
cancelled at 1.50 s
status: Cancelled
triangles now 214900 (partial)

A cancelled decimation has done fewer collapses, not an invalid half-collapse; the mesh it leaves is smaller than the input and entirely usable.

When it goes wrong

Thinking cancel means failure

Status::Cancelled is a normal outcome, not an error; the mesh is valid and the caller decides what to do with the partial result.

A non-thread-safe callback

The callback is invoked from the calling thread only, even with threads above one, so it needs no locking - but do not assume it fires on a worker.

Comparing stage text by pointer across builds

stage is a literal, safe to compare by pointer within one build; compare the text if the pointer might cross a library boundary.

Variations

Report, do not cancel

Return true always and use the callback purely to drive a progress bar.

Cancel on a signal

Check an atomic flag inside the callback so an operator can stop a batch job between about every two percent.

Symbols used here

• rf::Progress
• rf::Decimator
• rf::DecimateReport