added yield to Thread

Author: tgymnich

Sources/TSCBasic/Thread.swift

@@ -65,6 +65,15 @@ final public class Thread {
             }
         }
     }
+
+    /// Causes the calling thread to yield execution to another thread.
+    public static func yield() {
+        #if os(Windows)
+          SwitchToThread()
+        #else
+          sched_yield()
+        #endif
+    }
 }
 
 #if canImport(Darwin)

Tests/TSCBasicTests/LockTests.swift

@@ -69,7 +69,7 @@ class LockTests: XCTestCase {
                         // Sum and write back to file.
                         try localFileSystem.writeFileContents(fileA, bytes: ByteString(encodingAsUTF8: String(valueA + 1)))
 
-                        sched_yield()
+                        Thread.yield()
 
                         // Get thr current contents of the file if any.
                         let valueB: Int
@@ -89,7 +89,7 @@ class LockTests: XCTestCase {
                     try! lock.withLock(type: .shared) {
                         try XCTAssertEqual(localFileSystem.readFileContents(fileA), localFileSystem.readFileContents(fileB))
 
-                        sched_yield()
+                        Thread.yield()
 
                         try XCTAssertEqual(localFileSystem.readFileContents(fileA), localFileSystem.readFileContents(fileB))
                     }