RAR does not write to cache file on rebuilds

[cdmihai]

Closes #2687

Cause of the issue:

• RAR uses two caches: a process wide cache and a project specific cache
• The project specific cache is serialized and reused between processes, whereas the process wide cache is not serialized. The process wide cache aggregates the project specific caches as projects are built.
• On every RAR execution, the project specific cache is loaded from disk, and compared against the value process wide cache: https://github.com/Microsoft/msbuild/blob/99d4c838624293725bfbfd1ae75405ec1bb99c4a/src/Tasks/SystemState.cs#L343-L351
• since the project wide cache is deserialized each time, its entries' are different instances from the entries in the process wide cache. This makes the reference equality check fail, and leads to dirtying the cache.

Fix: I chose to reuse the old code, wrap it with a guarding collection (to ensure an entry is checked for staleness only once), and ported over the change to replace stale entries from the process wide cache. Did this because the old code had an extra optimization: if the process wide cache had a more recent entry than the project specific cache, it would update the project specific cache from the process cache.

Before / After memory

Before / After CPU

[cdmihai]

@davkean

[davkean]

I likely regressed this.

[cdmihai]

Nothing interesting here. Build time suggests positive improvement, as every case seems to be an improvement, with largest in the mvc project which is RAR heavy.

Evaluation: Time (ms)

Test	Overall	Significant δ	Value
DotnetConsoleProject	✅	yes	95.1051 -> 94.1112 (-1.045%)
DotnetWebProject	🔴	yes	137.2171 -> 137.8964 (0.495%)
DotnetMvcProject	✅	yes	163.5339 -> 160.2404 (-2.014%)
Picasso	✅	yes	778.1822 -> 757.3825 (-2.673%)
SmallP2POldCsproj	✅	yes	135.6276 -> 132.9834 (-1.95%)
SmallP2PNewCsproj	✅	yes	244.8956 -> 242.6864 (-0.902%)
Generated_100_100_v150	👌	no	1595.2215 -> 1603.8711 (0.542%)
LargeP2POldCsproj	::ok_hand:	no	2245.3647 -> 2243.9941 (-0.061%)
roslyn	🔴	yes	9342.4617 -> 9518.1423 (1.88%)

Evaluation: Memory (bytes)

Test	Overall	Significant δ	Value
DotnetConsoleProject	::ok_hand:	no	5092600 -> 5091897 (-0.014%)
DotnetWebProject	::ok_hand:	no	6767956 -> 6767334 (-0.009%)
DotnetMvcProject	::ok_hand:	no	7612326 -> 7611534 (-0.01%)
Picasso	::ok_hand:	no	33896648 -> 33896578 (0%)
SmallP2POldCsproj	👌	no	6107778 -> 6107937 (0.003%)
SmallP2PNewCsproj	::ok_hand:	no	10552742 -> 10552735 (0%)
Generated_100_100_v150	::ok_hand:	no	140411739 -> 140411333 (0%)
LargeP2POldCsproj	👌	no	83129678 -> 83130926 (0.002%)
roslyn	::ok_hand:	no	398736024 -> 397053171 (-0.422%)

Build: Time (ms)

Test	Overall	Significant δ	Value
DotnetConsoleProject	::ok_hand:	no	23.6024 -> 23.497 (-0.447%)
DotnetWebProject	👌	no	28.2513 -> 28.2599 (0.03%)
DotnetMvcProject	✅	yes	31.5754 -> 30.8451 (-2.313%)
Picasso	✅	yes	4584.9235 -> 4537.6154 (-1.032%)
SmallP2POldCsproj	✅	yes	199.8064 -> 198.7935 (-0.507%)
SmallP2PNewCsproj	✅	yes	176.9933 -> 175.8262 (-0.659%)

Build: Memory (bytes)

Test	Overall	Significant δ	Value
DotnetConsoleProject	✅	yes	1166317 -> 1165472 (-0.072%)
DotnetWebProject	🔴	yes	1310784 -> 1312840 (0.157%)
DotnetMvcProject	👌	no	1484924 -> 1485014 (0.006%)
Picasso	👌	no	194598709 -> 195218981 (0.319%)
SmallP2POldCsproj	✅	yes	8185243 -> 8179606 (-0.069%)
SmallP2PNewCsproj	👌	no	7256183 -> 7259937 (0.052%)

[AndyGerlicher]

Approved, @cdmihai merge it please.