Merge pull request #36 from cwakamo/safe-view-logging-in-the-background

[PlaygroundLogger] Make NSView and UIView logging short-circuit if no…

Author: cwakamo

PlaygroundLogger/PlaygroundLogger/OpaqueRepresentations/AppKit/NSView+OpaqueImageRepresentable.swift

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2017-2018 Apple Inc. and the Swift project authors
+// Copyright (c) 2017-2019 Apple Inc. and the Swift project authors
 // Licensed under Apache License v2.0 with Runtime Library Exception
 //
 // See http://swift.org/LICENSE.txt for license information
@@ -15,6 +15,12 @@
 
     extension NSView: OpaqueImageRepresentable {
         func encodeImage(into encoder: LogEncoder, withFormat format: LogEncoder.Format) throws {
+            guard Thread.isMainThread else {
+                // If we're not on the main thread, then just encode empty PNG data.
+                encoder.encode(number: 0)
+                return
+            }
+
             guard let bitmapRep = self.bitmapImageRepForCachingDisplay(in: self.bounds) else {
                 if self.bounds == .zero {
                     // If we couldn't get a bitmap representation because the view is zero-sized, encode empty PNG data.

PlaygroundLogger/PlaygroundLogger/OpaqueRepresentations/UIKit/UIView+OpaqueImageRepresentable.swift

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2017-2018 Apple Inc. and the Swift project authors
+// Copyright (c) 2017-2019 Apple Inc. and the Swift project authors
 // Licensed under Apache License v2.0 with Runtime Library Exception
 //
 // See http://swift.org/LICENSE.txt for license information
@@ -15,6 +15,12 @@
 
     extension UIView: OpaqueImageRepresentable {
         func encodeImage(into encoder: LogEncoder, withFormat format: LogEncoder.Format) {
+            guard Thread.isMainThread else {
+                // If we're not on the main thread, then just encode empty PNG data.
+                encoder.encode(number: 0)
+                return
+            }
+
             let ir = UIGraphicsImageRenderer(size: bounds.size)
             let pngData = ir.pngData { _ in
                 self.drawHierarchy(in: bounds, afterScreenUpdates: true)

PlaygroundLogger/PlaygroundLoggerTests/LogEntryTests.swift

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2018 Apple Inc. and the Swift project authors
+// Copyright (c) 2018-2019 Apple Inc. and the Swift project authors
 // Licensed under Apache License v2.0 with Runtime Library Exception
 //
 // See http://swift.org/LICENSE.txt for license information
@@ -81,6 +81,51 @@ class LogEntryTests: XCTestCase {
         try logEntry.encode(with: encoder, format: .current)
     }
 
+    func testViewBackgroundThread() throws {
+        #if os(macOS)
+            let view = NSView(frame: NSRect(x: 0, y: 0, width: 100, height: 100))
+        #elseif os(iOS) || os(tvOS)
+            let view = UIView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
+        #endif
+
+        func testLoggingOfView() throws {
+            let logEntry = try LogEntry(describing: view, name: "view", policy: .default)
+
+            guard case let .opaque(name, _, _, _, representation) = logEntry else {
+                XCTFail("Expected an opaque log entry")
+                return
+            }
+
+            XCTAssertEqual(name, "view")
+            XCTAssert(representation is ImageOpaqueRepresentation)
+
+            // Try to encode the log entry. This operation shouldn't throw; if it does, it will fail the test.
+            let encoder = LogEncoder()
+            try logEntry.encode(with: encoder, format: .current)
+        }
+
+        try testLoggingOfView()
+
+        var backgroundTestSucceeded = false
+        let expectation = self.expectation(description: "Background logging expectation")
+
+        DispatchQueue.global().async {
+            do {
+                try testLoggingOfView()
+                backgroundTestSucceeded = true
+            }
+            catch {
+                XCTFail("Logging the view failed")
+            }
+
+            expectation.fulfill()
+        }
+
+        self.wait(for: [expectation], timeout: 5)
+
+        XCTAssertTrue(backgroundTestSucceeded)
+    }
+
     func testLargeSet() throws {
         let set = Set(1...1000)