From 86fae9d32b0465f21312cdbfd3e477011aff7465 Mon Sep 17 00:00:00 2001
From: Nathan Daly <nhdaly@gmail.com>
Date: Thu, 19 Aug 2021 10:46:12 -0400
Subject: [PATCH] Add test for concurrent compile() and TimeZone construction.

Add comments
---
 src/types/timezone.jl |  4 +++
 test/thread-safety.jl | 68 ++++++++++++++++++++++++++-----------------
 2 files changed, 46 insertions(+), 26 deletions(-)

diff --git a/src/types/timezone.jl b/src/types/timezone.jl
index 01eb5fb07..25d36c363 100644
--- a/src/types/timezone.jl
+++ b/src/types/timezone.jl
@@ -1,3 +1,7 @@
+# Thread-local TimeZone cache, which caches time zones _per thread_, allowing thread-safe
+# caching. Note that this means the cache will grow in size, and may store redundant objects
+# accross multiple threads, but this extra space usage allows for fast, lock-free access
+# to the cache, while still being thread-safe.
 const THREAD_TZ_CACHES = Dict{String,Tuple{TimeZone,Class}}[]
 
 # Based upon the thread-safe Global RNG implementation in the Random stdlib:
diff --git a/test/thread-safety.jl b/test/thread-safety.jl
index c945075aa..b2028e590 100644
--- a/test/thread-safety.jl
+++ b/test/thread-safety.jl
@@ -10,39 +10,55 @@ using Test
 
 @assert Threads.nthreads() > 1 "This system does not support multiple threads, so the thread-safety tests cannot be run."
 
-function create_zdt(year, month, day, tz_name)
-    ZonedDateTime(DateTime(year, month, day), TimeZone(tz_name))
-end
-function cycle_zdts()
-    return [
-        try
-            create_zdt(year, month, day, tz_name)
-        catch e
-            e isa Union{ArgumentError,NonExistentTimeError} || rethrow()
-            nothing
+@testset "Multithreaded TimeZone brute force test" begin
+    function create_zdt(year, month, day, tz_name)
+        ZonedDateTime(DateTime(year, month, day), TimeZone(tz_name))
+    end
+    function cycle_zdts()
+        return [
+            try
+                create_zdt(year, month, day, tz_name)
+            catch e
+                # Ignore ZonedDateTimes that aren't valid
+                e isa Union{ArgumentError,AmbiguousTimeError,NonExistentTimeError} || rethrow()
+                nothing
+            end
+            for year in 2000:2020
+            for month in 1:5
+            for day in 10:15
+            for tz_name in timezone_names()
+        ]
+    end
+
+    outputs = Channel(Inf)
+    @sync begin
+        for _ in 1:15
+            Threads.@spawn begin
+                put!(outputs, cycle_zdts())
+            end
         end
-        for year in 2000:2020
-        for month in 1:5
-        for day in 10:15
-        for tz_name in timezone_names()
-    ]
+    end
+    close(outputs)
+
+    tzs = collect(outputs)
+
+    # Test that every Task produced the same result
+    allsame(x) = all(y -> y == first(x), x)
+    @test allsame(tzs)
 end
 
-const outputs = Channel(Inf)
-@sync begin
-    for _ in 1:15
+#----------------------------------------------------
+
+@testset "Interleaved compile() and TimeZone construction" begin
+    @sync for i in 1:20
+        if (i % 5 == 0)
+            TimeZones.TZData.compile()
+        end
         Threads.@spawn begin
-            put!(outputs, cycle_zdts())
+            TimeZone("US/Eastern", TimeZones.Class(:LEGACY))
         end
     end
 end
-close(outputs)
-
-const tzs = collect(outputs)
-
-# Test that every Task produced the same result
-allsame(x) = all(y -> y == first(x), x)
-@test allsame(tzs)
 """
 
 @info "Running Thread Safety tests"