<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Hi,<div class=""><br class=""></div><div class="">I’m porting some C to Swift and I need to pass a Swift instance through a `void *` (ie, UnsafeMutableRawPointer). It works, in one thread, but when a second thread accesses the exact same pointer, it fails with memory errors like EXC_BAD_ACCESS</div><div class=""><br class=""></div><div class="">The code below could be pasted into an AppDelegate.swift in a new single view iOS project. </div><div class=""><br class=""></div><div class="">Anyone know what’s going on here? The second call to `tryUsingUnsafePointer`, in the new thread, crashes.</div><div class=""><br class=""></div><div class="">Rob</div><div class=""><br class=""></div><div class=""><div style="margin: 0px; line-height: normal; font-family: Menlo;" class=""><div style="margin: 0px; line-height: normal;" class=""><br class=""></div><div style="margin: 0px; line-height: normal;" class=""><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">class</span><span style="font-variant-ligatures: no-common-ligatures" class=""> PointerTest {</span></div><p style="margin: 0px; line-height: normal; min-height: 14px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> str = </span><span style="font-variant-ligatures: no-common-ligatures; color: #d12f1b" class="">"Hello"</span></div><p style="margin: 0px; line-height: normal; min-height: 14px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">init</span><span style="font-variant-ligatures: no-common-ligatures" class="">() {</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(62, 30, 129);" class="">print</span><span style="font-variant-ligatures: no-common-ligatures;" class="">(</span><span style="color: rgb(209, 47, 27); font-variant-ligatures: no-common-ligatures;" class="">"PointerTest.init"</span><span style="font-variant-ligatures: no-common-ligatures;" class="">)</span> } </div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">deinit</span><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(62, 30, 129);" class="">print</span><span style="font-variant-ligatures: no-common-ligatures;" class="">(</span><span style="color: rgb(209, 47, 27); font-variant-ligatures: no-common-ligatures;" class="">"PointerTest.deinit"</span><span style="font-variant-ligatures: no-common-ligatures;" class="">)</span> }</div><p style="margin: 0px; line-height: normal; min-height: 14px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">func</span><span style="font-variant-ligatures: no-common-ligatures" class=""> start() {</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">var</span><span style="font-variant-ligatures: no-common-ligatures" class=""> mSelf = </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">self</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> unsafePtr = </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">UnsafeMutableRawPointer</span><span style="font-variant-ligatures: no-common-ligatures" class="">(&mSelf)</span></div><div style="margin: 0px; line-height: normal; color: rgb(49, 89, 93);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">tryUsingUnsafePointer</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">(unsafePtr)</span></div><div style="margin: 0px; line-height: normal; color: rgb(209, 47, 27);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #3e1e81" class="">print</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">(</span><span style="font-variant-ligatures: no-common-ligatures" class="">"Passing unsafe pointer to another thread: </span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">\</span><span style="font-variant-ligatures: no-common-ligatures" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">unsafePtr</span><span style="font-variant-ligatures: no-common-ligatures" class="">)"</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">)</span> </div><div style="margin: 0px; line-height: normal; color: rgb(62, 30, 129);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Thread</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">.</span><span style="font-variant-ligatures: no-common-ligatures" class="">detachNewThread</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> {</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">tryUsingUnsafePointer</span><span style="font-variant-ligatures: no-common-ligatures" class="">(unsafePtr)</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">}</span></div><div style="margin: 0px; line-height: normal; min-height: 14px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">func</span><span style="font-variant-ligatures: no-common-ligatures" class=""> tryUsingUnsafePointer(</span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">_</span><span style="font-variant-ligatures: no-common-ligatures" class=""> ptr: </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">UnsafeMutableRawPointer</span><span style="font-variant-ligatures: no-common-ligatures" class="">) {</span></div><div style="margin: 0px; line-height: normal; color: rgb(209, 47, 27);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #3e1e81" class="">print</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">(</span><span style="font-variant-ligatures: no-common-ligatures" class="">"Using unsafe pointer:"</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">)</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> typedPtr = ptr.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3e1e81" class="">assumingMemoryBound</span><span style="font-variant-ligatures: no-common-ligatures" class="">(to: </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">PointerTest</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class="">)</span></div><div style="margin: 0px; line-height: normal; color: rgb(0, 132, 0);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">// let typedPtr = ptr.bindMemory(to: PointerTest.self, capacity: 1)</span></div><div style="margin: 0px; line-height: normal; color: rgb(209, 47, 27);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #3e1e81" class="">print</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">(</span><span style="font-variant-ligatures: no-common-ligatures" class="">" typedPtr: </span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">\</span><span style="font-variant-ligatures: no-common-ligatures" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">typedPtr</span><span style="font-variant-ligatures: no-common-ligatures" class="">)"</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">)</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> obj = typedPtr.</span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">pointee</span></div><div style="margin: 0px; line-height: normal; color: rgb(0, 132, 0);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #3e1e81" class="">print</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #d12f1b" class="">" obj.str: </span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">\</span><span style="font-variant-ligatures: no-common-ligatures; color: #d12f1b" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">obj.</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">str</span><span style="font-variant-ligatures: no-common-ligatures; color: #d12f1b" class="">)"</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">) </span><span style="font-variant-ligatures: no-common-ligatures" class="">// Memory error happening here, or sometimes line above</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">}</span></div><div style="margin: 0px; line-height: normal; min-height: 14px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; min-height: 14px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; color: rgb(186, 45, 162);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">@UIApplicationMain</span></div><div style="margin: 0px; line-height: normal; color: rgb(112, 61, 170);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">class</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> AppDelegate: </span><span style="font-variant-ligatures: no-common-ligatures" class="">UIResponder</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">, </span><span style="font-variant-ligatures: no-common-ligatures" class="">UIApplicationDelegate</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> {</span></div><div style="margin: 0px; line-height: normal; min-height: 14px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">var</span><span style="font-variant-ligatures: no-common-ligatures" class=""> window: </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">UIWindow</span><span style="font-variant-ligatures: no-common-ligatures" class="">?</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">var</span><span style="font-variant-ligatures: no-common-ligatures" class=""> ptrTest: </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">PointerTest</span><span style="font-variant-ligatures: no-common-ligatures" class="">?</span></div><div style="margin: 0px; line-height: normal; min-height: 14px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">func</span><span style="font-variant-ligatures: no-common-ligatures" class=""> application(</span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">_</span><span style="font-variant-ligatures: no-common-ligatures" class=""> application: </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">UIApplication</span><span style="font-variant-ligatures: no-common-ligatures" class="">, didFinishLaunchingWithOptions launchOptions: [</span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">UIApplicationLaunchOptionsKey</span><span style="font-variant-ligatures: no-common-ligatures" class="">: </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">Any</span><span style="font-variant-ligatures: no-common-ligatures" class="">]?) -> </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Bool</span><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; line-height: normal; min-height: 14px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; color: rgb(79, 129, 135);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">ptrTest</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> = </span><span style="font-variant-ligatures: no-common-ligatures" class="">PointerTest</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">()</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">ptrTest</span><span style="font-variant-ligatures: no-common-ligatures" class="">?.</span><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">start</span><span style="font-variant-ligatures: no-common-ligatures" class="">()</span></div><div style="margin: 0px; line-height: normal; min-height: 14px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; color: rgb(186, 45, 162);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">return</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">true</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class="">[...]</span></div></div></div></div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><br class=""></div></body></html>