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makespan

Makespan

This Rust library implements several solvers for task scheduling problems optimizing makespan.

Graham's notation

Definitions of scheduling problems in operations research commonly use Graham's notation a|b|c where

  1. a defines machine environment (resources)
  2. b denotes task/job characteristics
  3. c specifies the objective function that is to be minimized (note that this library focuses on optimizing the makespan C_max)

Covered scheduling problems

The module structure of this library follows a structure of the general taxonomy of scheduling problems and as mentioned above focuses on minimizing the makespan (C_max).

General constraints:

  • Each task can be processed by at most one resource at a time
  • Each resource can process at most one task at a time

Single-processor

This class of scheduling problems considers single processing unit (resource).

Non-preemptive

This sub-class considers non-preemptive tasks and is covered by module sp. The list of problems and corresponding algorithms includes:

  • 1||C_max: optimal, linear
  • 1|prec|C_max: optimal, linear
  • 1|r_j|C_max: optimal, log-linear
  • 1|d'_j|C_max: EDF (optimal, log-linear)
  • 1|r_j,d'_j|C_max: heuristic (log-linear), Bratley's BnB (optimal)
  • 1|chains,r_j|C_max: special case with chains totally ordered (otpimal, linear)

Multi-processor

This class of scheduling problems considers multiple processing units (resources).

Non-preemptive

This sub-class considers non-preemptive tasks and is covered by module mp. The list of problems and corresponding algorithms includes:

  • P||C_max: LPT (approx), BnB (optimal)

Preemptive

This sub-class considers preemptive tasks and is covered by module mp_pmtn. The list of problems and corresponding algorithms includes:

  • P|pmtn|C_max: McNaughton (optimal)

Resources

License and version

Current version: 0.3.0

License: MIT OR Apache-2.0

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makespan's Issues

Rework benchmarks

Benchmarks currently do not compile and use unstable feature(test) macro. Rework them using for instance criterion.

Improve scheduling result

Re-introduce additional metadata in the scheduling result in addition to the Schedule.

For instance:

  • search statistics
  • approximation factor

More schedulers for parallel identical resources

Implement the more algorithms for parallel identical resources:

  • List Scheduling approximation algorithm for P|prec|C_max
  • Rothkopf's Dynamic Programming for P||C_max
  • Muntz&Coffman's Level Algorithm for P|pmtn,prec|C_max

Improve error reporting

Currently the resulting Schedule is simply wrapped in an Option context regardless of what happened during scheduling. It would be nice to have better (read: more informative) error reporting.

For instance:

  • Distinguish between invalid inputs (e.g. r=0 or empty p) and infeasible solutions
  • Distinguish internal errors produced by the scheduling algorithms (e.g. BnB search encounters partial solution but there are no remaining tasks)

Note that the latter case (internal errors) might be relevant for algorithm debugging but probably are not relevant to users.

Linear sorting

Consider re-introduction of linear sorting - e.g. using voracious_radix_sort.

Some algorithms would benefit from reduced asymptotic complexity but investigate the effect with benchmarks. One possibility would be to enable it only for large enough inputs or for certain T: Time types.

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