Remove cross-thread task lookup by task_id

[fknorr]

This PR is in preparation of the command lookahead feature, which will transparently avoid buffer resizes, but requires an arbitrary large task graph to be kept in memory, which is not possible with the bounded-capacity task_ring_buffer.

The old master-worker model required looking up tasks by task_id, so task_manager and task_ring_buffer provided this lookup functionality. This is no longer necessary, and the scheduler thread can be decoupled from task_manager by handling stable task pointers directly. This change simplifies the interactions between application thread and scheduler thread considerably.

• Task instances are now managed in the same epoch-based structure employed for instructions, and the ring buffer size limit is gone.
• Task-commands keep a const task* pointer directly, which is guaranteed to be live by the horizon mechanism. In the future task pointers can be introduced to instructions as well, avoiding kernel lambda copying.
• The initial epoch is now generated explicitly instead of implicitly in the task_manager constructor, so it can be treated like any other instruction, avoiding many special-casings.
• task_callback is replaced with a delegate interface, and [tci]dag_test_contexts can avoid manually constructing horizons.

[github-actions]

Check-perf-impact results: (e884a5b266877a2f8b1f68ea7d0b8bef)

❓ No new benchmark data submitted. ❓
Please re-run the microbenchmarks and include the results if your commit could potentially affect performance.

[coveralls]

Pull Request Test Coverage Report for Build 11609757631

Details

• 152 of 152 (100.0%) changed or added relevant lines in 15 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.05%) to 95.249%

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Files with Coverage Reduction	New Missed Lines	%
src/print_graph.cc	1	94.51%

Totals
Change from base Build 11603776400:	0.05%
Covered Lines:	6730
Relevant Lines:	6831

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💛 - Coveralls

[github-actions]

clang-tidy made some suggestions

[github-actions]

Check-perf-impact results: (da9a532564f4bc5510893652bf98be8b)

⚠️ Significant slowdown (>1.25x) in some microbenchmark results: benchmark intrusive graph dependency handling with N nodes - 100 / checking for dependencies, normalizing a fully mergeable tiling of boxes - 1 / large, embedded in 3d
➕ Added microbenchmark(s): task-graph, benchmark task handling / generating and deleting tasks
➖ Removed microbenchmark(s): task-graph, benchmark task handling > without access thread / generating and deleting tasks, task-graph, benchmark task handling > with access thread / generating and deleting tasks with access thread

Relative execution time per category: (mean of relative medians)

• command-graph : 1.02x
• graph-nodes : 1.05x
• grid : 1.04x
• instruction-graph : 1.01x
• scheduler : 1.04x
• system : 0.99x
• task-graph : 0.98x

[github-actions]

Check-perf-impact results: (2a3c70512edf780ef21985d30e324aa9)

🚀 Significant speedup (<0.80x) in some microbenchmark results: normalizing a fully mergeable tiling of boxes - 1 / large, native
➕ Added microbenchmark(s): task-graph, benchmark task handling / generating and deleting tasks
➖ Removed microbenchmark(s): task-graph, benchmark task handling > without access thread / generating and deleting tasks, task-graph, benchmark task handling > with access thread / generating and deleting tasks with access thread

Relative execution time per category: (mean of relative medians)

• command-graph : 0.96x
• graph-nodes : 1.00x
• grid : 1.02x
• instruction-graph : 0.98x
• scheduler : 1.01x
• system : 0.98x
• task-graph : 0.87x 🚀

[github-actions]

⚠️ Clang-Tidy found issue(s) with the introduced code (1/6)

[github-actions]

⚠️ Clang-Tidy found issue(s) with the introduced code (2/6)

[github-actions]

⚠️ Clang-Tidy found issue(s) with the introduced code (3/6)

[github-actions]

⚠️ Clang-Tidy found issue(s) with the introduced code (4/6)

[github-actions]

⚠️ Clang-Tidy found issue(s) with the introduced code (5/6)

[github-actions]

⚠️ Clang-Tidy found issue(s) with the introduced code (6/6)

[github-actions]

⚠️ Clang-Tidy found issue(s) with the introduced code (1/2)

[github-actions]

⚠️ Clang-Tidy found issue(s) with the introduced code (2/2)