From c6efca5a7f016dc3313698cc9a6077be43a864cd Mon Sep 17 00:00:00 2001
From: PetrGuan <peterguanjun1992@gmail.com>
Date: Thu, 12 May 2022 21:52:21 +0800
Subject: [PATCH 1/3] Add thread safety unit test for LazyCache

Add thread safety unit test for LazyCache
---
 Tests/TSCBasicTests/LazyCacheTests.swift | 46 +++++++++++++++++-------
 1 file changed, 34 insertions(+), 12 deletions(-)

diff --git a/Tests/TSCBasicTests/LazyCacheTests.swift b/Tests/TSCBasicTests/LazyCacheTests.swift
index 3c6b2540..8736542c 100644
--- a/Tests/TSCBasicTests/LazyCacheTests.swift
+++ b/Tests/TSCBasicTests/LazyCacheTests.swift
@@ -13,20 +13,19 @@ import XCTest
 import TSCBasic
 
 class LazyCacheTests: XCTestCase {
-    func testBasics() {
-        class Foo {
-            var numCalls = 0
-            
-            var bar: Int { return barCache.getValue(self) }
-            var barCache = LazyCache<Foo, Int>(someExpensiveMethod)
-            func someExpensiveMethod() -> Int {
-                numCalls += 1
-                return 42
-            }
-                
+    private class Foo {
+        var numCalls = 0
+
+        var bar: Int { return barCache.getValue(self) }
+        var barCache = LazyCache<Foo, Int>(someExpensiveMethod)
+        func someExpensiveMethod() -> Int {
+            numCalls += 1
+            return 42
         }
 
-        // FIXME: Make this a more interesting test once we have concurrency primitives.
+    }
+
+    func testBasics() {
         for _ in 0..<10 {
             let foo = Foo()
             XCTAssertEqual(foo.numCalls, 0)
@@ -36,4 +35,27 @@ class LazyCacheTests: XCTestCase {
             }
         }
     }
+
+    func testThreadSafety() {
+        let dispatchGroup = DispatchGroup()
+        let exp = expectation(description: "multi thread")
+        for _ in 0..<10 {
+            let foo = Foo()
+            for _ in 0..<10 {
+                dispatchGroup.enter()
+                DispatchQueue.global().async {
+                    XCTAssertEqual(foo.bar, 42)
+                    dispatchGroup.leave()
+
+                    XCTAssertEqual(foo.numCalls, 1)
+                }
+            }
+        }
+
+        dispatchGroup.notify(queue: .main) {
+            exp.fulfill()
+        }
+
+        wait(for: [exp], timeout: 0.5)
+    }
 }

From 33184d4678e664b755750edafdc6a2ba472c3ab1 Mon Sep 17 00:00:00 2001
From: PetrGuan <peterguanjun1992@gmail.com>
Date: Thu, 12 May 2022 22:00:25 +0800
Subject: [PATCH 2/3] Update LazyCacheTests.swift

---
 Tests/TSCBasicTests/LazyCacheTests.swift | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Tests/TSCBasicTests/LazyCacheTests.swift b/Tests/TSCBasicTests/LazyCacheTests.swift
index 8736542c..7e96c309 100644
--- a/Tests/TSCBasicTests/LazyCacheTests.swift
+++ b/Tests/TSCBasicTests/LazyCacheTests.swift
@@ -56,6 +56,6 @@ class LazyCacheTests: XCTestCase {
             exp.fulfill()
         }
 
-        wait(for: [exp], timeout: 0.5)
+        wait(for: [exp], timeout: 0.2)
     }
 }

From 2e5b0c1c0793011148b633ba5c11fcb490860733 Mon Sep 17 00:00:00 2001
From: PetrGuan <peterguanjun1992@gmail.com>
Date: Wed, 15 Jun 2022 20:23:33 +0800
Subject: [PATCH 3/3] Pass dispatchGroup to DispatchQueue instead

---
 Tests/TSCBasicTests/LazyCacheTests.swift | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/Tests/TSCBasicTests/LazyCacheTests.swift b/Tests/TSCBasicTests/LazyCacheTests.swift
index 7e96c309..f364ee33 100644
--- a/Tests/TSCBasicTests/LazyCacheTests.swift
+++ b/Tests/TSCBasicTests/LazyCacheTests.swift
@@ -39,14 +39,12 @@ class LazyCacheTests: XCTestCase {
     func testThreadSafety() {
         let dispatchGroup = DispatchGroup()
         let exp = expectation(description: "multi thread")
+
         for _ in 0..<10 {
             let foo = Foo()
             for _ in 0..<10 {
-                dispatchGroup.enter()
-                DispatchQueue.global().async {
+                DispatchQueue.global().async(group: dispatchGroup) {
                     XCTAssertEqual(foo.bar, 42)
-                    dispatchGroup.leave()
-
                     XCTAssertEqual(foo.numCalls, 1)
                 }
             }