Revert "remove dispatch declarations; use CLinuxGCD"

This reverts commit af0b5e9.

Author: lhoward

Package.resolved

@@ -53,7 +53,6 @@ let package = Package(
     .package(url: "https://github.com/apple/swift-log", from: "1.6.2"),
     .package(url: "https://github.com/apple/swift-system", from: "1.0.0"),
     .package(url: "https://github.com/PADL/SocketAddress", from: "0.0.1"),
-    .package(url: "https://github.com/PADL/CLinuxGCD", from: "6.0.2"),
   ],
   targets: [
     .systemLibrary(
@@ -62,10 +61,7 @@ let package = Package(
     ),
     .target(
       name: "CIORingShims",
-      dependencies: ["CIOURing",
-                     .product(name: "CBlockHeaders", package: "CLinuxGCD"),
-                     .product(name: "CDispatchHeaders", package: "CLinuxGCD")
-      ],
+      dependencies: ["CIOURing"],
       cSettings: [
         .define("_XOPEN_SOURCE=700"),
         .define("_DEFAULT_SOURCE"),
@@ -147,6 +143,8 @@ let package = Package(
       name: "IORingDeviceSpy",
       dependencies: ["IORing", "IORingUtils"],
       path: "Examples/IORingDeviceSpy"
-    )
-  ]
+    ),
+  ],
+  cLanguageStandard: .c18,
+  cxxLanguageStandard: .cxx20
 )

Package.swift

@@ -28,7 +28,41 @@ extern "C" void *_Block_copy(const void *);
 extern "C" void _Block_release(const void *);
 #endif
 
+#if __has_include(<dispatch/dispatch.h>)
 #include <dispatch/dispatch.h>
+#else
+// on Linux dispatch/dispatch.h is only available with unsafe Swift flags,
+// which preclude the use of this package as a versioned dependency
+struct dispatch_source_type_s {} __attribute__((aligned(sizeof(uintptr_t))));
+
+typedef struct dispatch_source_s *dispatch_source_t;
+typedef struct dispatch_queue_s *dispatch_queue_t;
+typedef const struct dispatch_source_type_s *dispatch_source_type_t;
+
+typedef void (^dispatch_block_t)(void);
+
+extern "C" {
+  extern const struct dispatch_source_type_s _dispatch_source_type_read;
+
+  void dispatch_release(void *object);
+  void dispatch_resume(void *object);
+
+  void *dispatch_get_context(void *object);
+  void dispatch_set_context(void *object, void *context);
+
+  void dispatch_source_cancel(void *object);
+  void dispatch_source_set_event_handler(dispatch_source_t source, dispatch_block_t handler);
+  void dispatch_source_set_cancel_handler(dispatch_source_t source, dispatch_block_t handler);
+
+  dispatch_queue_t dispatch_get_global_queue(intptr_t identifier, uintptr_t flags);
+  dispatch_source_t dispatch_source_create(dispatch_source_type_t type, uintptr_t handle, uintptr_t mask, dispatch_queue_t queue);
+}
+
+#define dispatch_cancel dispatch_source_cancel
+#define DISPATCH_QUEUE_PRIORITY_DEFAULT 0
+#define DISPATCH_SOURCE_TYPE_READ (&_dispatch_source_type_read)
+
+#endif
 
 #include "CIORingShims.h"