Merge pull request swiftlang#39160 from mikeash/voucher-propagation-5.5

[5.5][Concurrency] Propagate Darwin vouchers across async tasks.

Author: mikeash

include/swift/ABI/Task.h

@@ -23,6 +23,7 @@
 #include "swift/ABI/Metadata.h"
 #include "swift/ABI/MetadataValues.h"
 #include "swift/Runtime/Config.h"
+#include "swift/Runtime/VoucherShims.h"
 #include "swift/Basic/STLExtras.h"
 #include "bitset"
 #include "queue" // TODO: remove and replace with our own mpsc
@@ -72,7 +73,13 @@ class alignas(2 * alignof(void*)) Job :
   // Derived classes can use this to store a Job Id.
   uint32_t Id = 0;
 
-  void *Reserved[2] = {};
+  /// The voucher associated with the job. Note: this is currently unused on
+  /// non-Darwin platforms, with stub implementations of the functions for
+  /// consistency.
+  voucher_t Voucher = nullptr;
+
+  /// Reserved for future use.
+  void *Reserved = nullptr;
 
   // We use this union to avoid having to do a second indirect branch
   // when resuming an asynchronous task, which we expect will be the
@@ -88,23 +95,32 @@ class alignas(2 * alignof(void*)) Job :
   Job(JobFlags flags, JobInvokeFunction *invoke,
       const HeapMetadata *metadata = &jobHeapMetadata)
       : HeapObject(metadata), Flags(flags), RunJob(invoke) {
+    Voucher = voucher_copy();
     assert(!isAsyncTask() && "wrong constructor for a task");
   }
 
   Job(JobFlags flags, TaskContinuationFunction *invoke,
-      const HeapMetadata *metadata = &jobHeapMetadata)
+      const HeapMetadata *metadata = &jobHeapMetadata,
+      bool captureCurrentVoucher = true)
       : HeapObject(metadata), Flags(flags), ResumeTask(invoke) {
+    if (captureCurrentVoucher)
+      Voucher = voucher_copy();
     assert(isAsyncTask() && "wrong constructor for a non-task job");
   }
 
   /// Create a job with "immortal" reference counts.
   /// Used for async let tasks.
   Job(JobFlags flags, TaskContinuationFunction *invoke,
-      const HeapMetadata *metadata, InlineRefCounts::Immortal_t immortal)
+      const HeapMetadata *metadata, InlineRefCounts::Immortal_t immortal,
+      bool captureCurrentVoucher = true)
       : HeapObject(metadata, immortal), Flags(flags), ResumeTask(invoke) {
+    if (captureCurrentVoucher)
+      Voucher = voucher_copy();
     assert(isAsyncTask() && "wrong constructor for a non-task job");
   }
 
+  ~Job() { swift_voucher_release(Voucher); }
+
   bool isAsyncTask() const {
     return Flags.isAsyncTask();
   }
@@ -229,8 +245,9 @@ class AsyncTask : public Job {
   /// Private.initialize separately.
   AsyncTask(const HeapMetadata *metadata, JobFlags flags,
             TaskContinuationFunction *run,
-            AsyncContext *initialContext)
-    : Job(flags, run, metadata),
+            AsyncContext *initialContext,
+            bool captureCurrentVoucher)
+    : Job(flags, run, metadata, captureCurrentVoucher),
       ResumeContext(initialContext) {
     assert(flags.isAsyncTask());
     Id = getNextTaskId();
@@ -243,8 +260,9 @@ class AsyncTask : public Job {
   AsyncTask(const HeapMetadata *metadata, InlineRefCounts::Immortal_t immortal,
             JobFlags flags,
             TaskContinuationFunction *run,
-            AsyncContext *initialContext)
-    : Job(flags, run, metadata, immortal),
+            AsyncContext *initialContext,
+            bool captureCurrentVoucher)
+    : Job(flags, run, metadata, immortal, captureCurrentVoucher),
       ResumeContext(initialContext) {
     assert(flags.isAsyncTask());
     Id = getNextTaskId();

include/swift/Runtime/VoucherShims.h

@@ -0,0 +1,102 @@
+//===--- VoucherShims.h - Shims for OS vouchers --------------------*- C++ -*-//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2021 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+//
+// Shims for interfacing with OS voucher calls.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_CONCURRENCY_VOUCHERSHIMS_H
+#define SWIFT_CONCURRENCY_VOUCHERSHIMS_H
+
+#include "Config.h"
+
+// swift-corelibs-libdispatch has os/voucher_private.h but it doesn't work for
+// us yet, so only look for it on Apple platforms.
+#if __APPLE__ && __has_include(<os/voucher_private.h>)
+#define SWIFT_HAS_VOUCHER_HEADER 1
+#include <os/voucher_private.h>
+#endif
+
+// A "dead" voucher pointer, indicating that a voucher has been removed from
+// a Job, distinct from a NULL voucher that could just mean no voucher was
+// present. This allows us to catch problems like adopting a voucher from the
+// same Job twice without restoring it.
+#define SWIFT_DEAD_VOUCHER ((voucher_t)-1)
+
+// The OS has voucher support if it has the header or if it has ObjC interop.
+#if SWIFT_HAS_VOUCHER_HEADER || SWIFT_OBJC_INTEROP
+#define SWIFT_HAS_VOUCHERS 1
+#endif
+
+#if SWIFT_HAS_VOUCHERS
+
+#if SWIFT_HAS_VOUCHER_HEADER
+
+#else
+
+// If the header isn't available, declare the necessary calls here.
+
+#include <os/object.h>
+
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wgnu-zero-variadic-macro-arguments"
+OS_OBJECT_DECL_CLASS(voucher);
+#pragma clang diagnostic pop
+
+extern "C" voucher_t _Nullable voucher_copy(void);
+
+// Consumes argument, returns retained value.
+extern "C" voucher_t _Nullable voucher_adopt(voucher_t _Nullable voucher);
+
+#endif // __has_include(<os/voucher_private.h>)
+
+static inline void swift_voucher_release(voucher_t _Nullable voucher) {
+  // This NULL check isn't necessary, but NULL vouchers will be common, so
+  // optimize for that.
+  if (!voucher)
+    return;
+  if (voucher == SWIFT_DEAD_VOUCHER)
+    return;
+  os_release(voucher);
+}
+
+#else  // __APPLE__
+
+// Declare some do-nothing stubs for OSes without voucher support.
+typedef void *voucher_t;
+static inline voucher_t _Nullable voucher_copy(void) { return nullptr; }
+static inline voucher_t _Nullable voucher_adopt(voucher_t _Nullable voucher) {
+  return nullptr;
+}
+static inline void swift_voucher_release(voucher_t _Nullable voucher) {}
+#endif // __APPLE__
+
+// Declare our own voucher_needs_adopt for when we don't get it from the SDK.
+// This declaration deliberately takes `void *` instead of `voucher_t`. When the
+// SDK provides one that takes `voucher_t`, then C++ overload resolution will
+// favor that one. When the SDK does not provide a declaration, then the call
+// site will invoke this stub instead.
+static inline bool voucher_needs_adopt(void * _Nullable voucher) {
+  return true;
+}
+
+static inline bool swift_voucher_needs_adopt(voucher_t _Nullable voucher) {
+#if __APPLE__
+  if (__builtin_available(macOS 12.0, iOS 15.0, tvOS 15.0, watchOS 8.0, *))
+    return voucher_needs_adopt(voucher);
+  return true;
+#else
+  return voucher_needs_adopt(voucher);
+#endif
+}
+
+#endif // SWIFT_CONCURRENCY_VOUCHERSHIMS_H