[Basic] Make DiagnosticsEngine thread safe

Author: aciidgh

Sources/Basic/DiagnosticsEngine.swift

@@ -8,6 +8,8 @@
  See http://swift.org/CONTRIBUTORS.txt for Swift project authors
 */
 
+import Dispatch
+
 /// A type which can be used as a diagnostic parameter.
 public protocol DiagnosticParameter {
 
@@ -250,18 +252,28 @@ public protocol DiagnosticsScope {
 }
 
 public class DiagnosticsEngine: CustomStringConvertible {
+
+ /// Queue to protect concurrent mutations to the diagnositcs engine.
+ private let queue = DispatchQueue(label: "\(DiagnosticsEngine.self)")
+
  /// The diagnostics produced by the engine.
- public var diagnostics: [Diagnostic] = []
+ public var diagnostics: [Diagnostic] {
+ return queue.sync { _diagnostics }
+ }
+ private var _diagnostics: [Diagnostic] = []
 
+ /// Returns true if there is an error diagnostics in the engine.
  public var hasErrors: Bool {
  return diagnostics.contains(where: { $0.behavior == .error })
  }
- 
+
  public init() {
  }
 
  public func emit(data: DiagnosticData, location: DiagnosticLocation) {
- diagnostics.append(Diagnostic(location: location, data: data))
+ queue.sync {
+ _diagnostics.append(Diagnostic(location: location, data: data))
+ }
  }
 
  /// Merges contents of given engine.