add atomic usage file test

Author: IanButterworth

test/pkg.jl

@@ -363,6 +363,30 @@ temp_pkg_dir() do project_path
         @test any(x -> startswith(x, manifest), keys(usage))
     end
 
+    @testset "atomic write_env_usage with $(Sys.CPU_THREADS) processes for 10 seconds" begin
+        tasks = Task[]
+        iobs = IOBuffer[]
+        Sys.CPU_THREADS == 1 && error("Cannot test for atomic usage log file interaction effectively with only Sys.CPU_THREADS=1")
+        for i in 1:Sys.CPU_THREADS
+            iob = IOBuffer()
+            t = @async run(pipeline(`$(Base.julia_cmd())
+                --project="$(pkgdir(Pkg))"
+                -e "import Pkg; t = Timer(10); while isopen(t) Pkg.activate(temp = true); Pkg.Types.EnvCache(); end"`,
+                stderr = iob, stdout = devnull))
+            push!(tasks, t)
+            push!(iobs, iob)
+        end
+        for i in eachindex(tasks)
+            try
+                fetch(tasks[i]) # If any of these failed it will throw when fetched
+            catch
+                print(String(take!(iobs[i])))
+                break
+            end
+        end
+        @test any(istaskfailed, tasks) == false
+    end
+
     @testset "adding nonexisting packages" begin
         nonexisting_pkg = randstring(14)
         @test_throws PkgError Pkg.add(nonexisting_pkg)