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Commit 8a8714c7 authored Apr 25, 2023 by Spandan Das

Do not modify input in-place

SortedUniqueStrings and FirstUniqueStrings dedupes repeating elements
and returns the deduped list. Currently, it also modifies the input list
in-place, which causes non-determinisitc failures like b/275313114

Operate on a copy of the input so that the input remains untouched.

SortedUniqueStrings is O(NlogN) and FirstUniqueStrings is ~O(N), so
creating a copy (O(N)) should not result in major performance regressions.
Numbers for this single unit test:
```
go test . -run TestStubsForLibraryInMultipleApexes -v -count 1000
Before: 174s
After: 172s
```

Test: go test ./android
Test: go test . -run TestStubsForLibraryInMultipleApexes -v -count 1000
Change-Id: Id859723b2c2ebdc0023876c4b6fabe75d870bad7

parent 00bafc66

android/apex.go

+2 −3

Original line number	Diff line number	Diff line
		@@ -513,9 +513,8 @@ func (m *ApexModuleBase) checkApexAvailableProperty(mctx BaseModuleContext) {
		// exactly the same set of APEXes (and platform), i.e. if their apex_available
		// properties have the same elements.
		func AvailableToSameApexes(mod1, mod2 ApexModule) bool {
		// Use CopyOf to prevent non-determinism (b/275313114#comment1)
		mod1ApexAvail := SortedUniqueStrings(CopyOf(mod1.apexModuleBase().ApexProperties.Apex_available))
		mod2ApexAvail := SortedUniqueStrings(CopyOf(mod2.apexModuleBase().ApexProperties.Apex_available))
		mod1ApexAvail := SortedUniqueStrings(mod1.apexModuleBase().ApexProperties.Apex_available)
		mod2ApexAvail := SortedUniqueStrings(mod2.apexModuleBase().ApexProperties.Apex_available)
		if len(mod1ApexAvail) != len(mod2ApexAvail) {
		return false
		}

android/util.go

+3 −0

Original line number	Diff line number	Diff line
		@@ -276,6 +276,8 @@ func RemoveFromList(s string, list []string) (bool, []string) {
		// FirstUniqueStrings returns all unique elements of a slice of strings, keeping the first copy of
		// each. It modifies the slice contents in place, and returns a subslice of the original slice.
		func FirstUniqueStrings(list []string) []string {
		// Do not moodify the input in-place, operate on a copy instead.
		list = CopyOf(list)
		// 128 was chosen based on BenchmarkFirstUniqueStrings results.
		if len(list) > 128 {
		return firstUniqueStringsMap(list)
		@@ -332,6 +334,7 @@ func LastUniqueStrings(list []string) []string {

		// SortedUniqueStrings returns what the name says
		func SortedUniqueStrings(list []string) []string {
		// FirstUniqueStrings creates a copy of `list`, so the input remains untouched.
		unique := FirstUniqueStrings(list)
		sort.Strings(unique)
		return unique