Allow building a concurrent libSwiftConcurrency without libdispatch

include/swift/Runtime/Concurrency.h

@@ -25,6 +25,22 @@
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wreturn-type-c-linkage"
 
+// Does the runtime use a cooperative global executor?
+#if defined(SWIFT_STDLIB_SINGLE_THREADED_RUNTIME)
+#define SWIFT_CONCURRENCY_COOPERATIVE_GLOBAL_EXECUTOR 1
+#else
+#define SWIFT_CONCURRENCY_COOPERATIVE_GLOBAL_EXECUTOR 0
+#endif
+
+// Does the runtime integrate with libdispatch?
+#ifndef SWIFT_CONCURRENCY_ENABLE_DISPATCH
+#if SWIFT_CONCURRENCY_COOPERATIVE_GLOBAL_EXECUTOR
+#define SWIFT_CONCURRENCY_ENABLE_DISPATCH 0
+#else
+#define SWIFT_CONCURRENCY_ENABLE_DISPATCH 1
+#endif
+#endif
+
 namespace swift {
 class DefaultActor;
 class TaskOptionRecord;
@@ -661,10 +677,14 @@ void swift_task_enqueueGlobalWithDelay(unsigned long long delay, Job *job);
 SWIFT_EXPORT_FROM(swift_Concurrency) SWIFT_CC(swift)
 void swift_task_enqueueMainExecutor(Job *job);
 
+#if SWIFT_CONCURRENCY_ENABLE_DISPATCH
+
 /// Enqueue the given job on the main executor.
 SWIFT_EXPORT_FROM(swift_Concurrency) SWIFT_CC(swift)
 void swift_task_enqueueOnDispatchQueue(Job *job, HeapObject *queue);
 
+#endif
+
 /// A hook to take over global enqueuing.
 typedef SWIFT_CC(swift) void (*swift_task_enqueueGlobal_original)(Job *job);
 SWIFT_EXPORT_FROM(swift_Concurrency)
@@ -806,6 +826,17 @@ void swift_task_reportUnexpectedExecutor(
 SWIFT_EXPORT_FROM(swift_Concurrency) SWIFT_CC(swift)
 JobPriority swift_task_getCurrentThreadPriority(void);
 
+#if SWIFT_CONCURRENCY_COOPERATIVE_GLOBAL_EXECUTOR
+
+/// Donate this thread to the global executor until either the
+/// given condition returns true or we've run out of cooperative
+/// tasks to run.
+SWIFT_EXPORT_FROM(swift_Concurrency) SWIFT_CC(swift)
+void swift_task_donateThreadToGlobalExecutorUntil(bool (*condition)(void*),
+                                                  void *context);
+
+#endif
+
 #ifdef __APPLE__
 /// A magic symbol whose address is the mask to apply to a frame pointer to
 /// signal that it is an async frame. Do not try to read the actual value of

stdlib/public/Concurrency/Actor.cpp

@@ -46,7 +46,7 @@
 #include "TaskPrivate.h"
 #include "VoucherSupport.h"
 
-#if !SWIFT_CONCURRENCY_COOPERATIVE_GLOBAL_EXECUTOR
+#if SWIFT_CONCURRENCY_ENABLE_DISPATCH
 #include <dispatch/dispatch.h>
 #endif
 

stdlib/public/Concurrency/CMakeLists.txt

@@ -35,6 +35,11 @@ endif()
 set(SWIFT_RUNTIME_CONCURRENCY_C_FLAGS)
 set(SWIFT_RUNTIME_CONCURRENCY_SWIFT_FLAGS)
 
+if(NOT SWIFT_CONCURRENCY_USES_DISPATCH)
+  list(APPEND SWIFT_RUNTIME_CONCURRENCY_C_FLAGS
+    "-DSWIFT_CONCURRENCY_ENABLE_DISPATCH=0")
+endif()
+
 if(NOT swift_concurrency_async_fp_mode)
   set(swift_concurrency_async_fp_mode "always")
 endif()

stdlib/public/Concurrency/GlobalExecutor.cpp

@@ -59,7 +59,7 @@
 #include "TaskPrivate.h"
 #include "Error.h"
 
-#if !SWIFT_CONCURRENCY_COOPERATIVE_GLOBAL_EXECUTOR
+#if SWIFT_CONCURRENCY_ENABLE_DISPATCH
 #include <dispatch/dispatch.h>
 
 #if !defined(_WIN32)
@@ -178,15 +178,21 @@ static Job *claimNextFromJobQueue() {
   }
 }
 
-void swift::donateThreadToGlobalExecutorUntil(bool (*condition)(void *),
-                                              void *conditionContext) {
+void swift::
+swift_task_donateThreadToGlobalExecutorUntil(bool (*condition)(void *),
+                                             void *conditionContext) {
   while (!condition(conditionContext)) {
     auto job = claimNextFromJobQueue();
     if (!job) return;
     swift_job_run(job, ExecutorRef::generic());
   }
 }
 
+#elif !SWIFT_CONCURRENCY_ENABLE_DISPATCH
+
+// No implementation.  The expectation is that integrators in this
+// configuration will hook all the appropriate functions.
+
 #else
 
 // Ensure that Job's layout is compatible with what Dispatch expects.
@@ -330,6 +336,9 @@ static void swift_task_enqueueGlobalImpl(Job *job) {
 
 #if SWIFT_CONCURRENCY_COOPERATIVE_GLOBAL_EXECUTOR
   insertIntoJobQueue(job);
+#elif !SWIFT_CONCURRENCY_ENABLE_DISPATCH
+  swift_reportError(0, "operation unsupported without libdispatch: "
+                       "swift_task_enqueueGlobal");
 #else
   // We really want four things from the global execution service:
   //  - Enqueuing work should have minimal runtime and memory overhead.
@@ -385,6 +394,9 @@ static void swift_task_enqueueGlobalWithDelayImpl(unsigned long long delay,
 
 #if SWIFT_CONCURRENCY_COOPERATIVE_GLOBAL_EXECUTOR
   insertIntoDelayedJobQueue(delay, job);
+#elif !SWIFT_CONCURRENCY_ENABLE_DISPATCH
+  swift_reportError(0, "operation unsupported without libdispatch: "
+                       "swift_task_enqueueGlobalWithDelay");
 #else
 
   dispatch_function_t dispatchFunction = &__swift_run_job;
@@ -419,6 +431,9 @@ static void swift_task_enqueueMainExecutorImpl(Job *job) {
 
 #if SWIFT_CONCURRENCY_COOPERATIVE_GLOBAL_EXECUTOR
   insertIntoJobQueue(job);
+#elif !SWIFT_CONCURRENCY_ENABLE_DISPATCH
+  swift_reportError(0, "operation unsupported without libdispatch: "
+                       "swift_task_enqueueMainExecutor");
 #else
 
   JobPriority priority = job->getPriority();
@@ -439,7 +454,7 @@ void swift::swift_task_enqueueMainExecutor(Job *job) {
     swift_task_enqueueMainExecutorImpl(job);
 }
 
-#if !SWIFT_CONCURRENCY_COOPERATIVE_GLOBAL_EXECUTOR
+#if SWIFT_CONCURRENCY_ENABLE_DISPATCH
 void swift::swift_task_enqueueOnDispatchQueue(Job *job,
                                               HeapObject *_queue) {
   JobPriority priority = job->getPriority();
@@ -449,7 +464,8 @@ void swift::swift_task_enqueueOnDispatchQueue(Job *job,
 #endif
 
 ExecutorRef swift::swift_task_getMainExecutor() {
-#if SWIFT_CONCURRENCY_COOPERATIVE_GLOBAL_EXECUTOR
+#if !SWIFT_CONCURRENCY_ENABLE_DISPATCH
+  // FIXME: this isn't right for the non-cooperative environment
   return ExecutorRef::generic();
 #else
   return ExecutorRef::forOrdinary(
@@ -459,7 +475,8 @@ ExecutorRef swift::swift_task_getMainExecutor() {
 }
 
 bool ExecutorRef::isMainExecutor() const {
-#if SWIFT_CONCURRENCY_COOPERATIVE_GLOBAL_EXECUTOR
+#if !SWIFT_CONCURRENCY_ENABLE_DISPATCH
+  // FIXME: this isn't right for the non-cooperative environment
   return isGeneric();
 #else
   return Identity == reinterpret_cast<HeapObject*>(&_dispatch_main_q);

stdlib/public/Concurrency/Task.cpp

@@ -27,7 +27,7 @@
 #include "Debug.h"
 #include "Error.h"
 
-#if !SWIFT_CONCURRENCY_COOPERATIVE_GLOBAL_EXECUTOR
+#if SWIFT_CONCURRENCY_ENABLE_DISPATCH
 #include <dispatch/dispatch.h>
 #endif
 
@@ -248,7 +248,7 @@ static void destroyTask(SWIFT_CONTEXT HeapObject *obj) {
 }
 
 static ExecutorRef executorForEnqueuedJob(Job *job) {
-#if SWIFT_CONCURRENCY_COOPERATIVE_GLOBAL_EXECUTOR
+#if !SWIFT_CONCURRENCY_ENABLE_DISPATCH
   return ExecutorRef::generic();
 #else
   void *jobQueue = job->SchedulerPrivate[Job::DispatchQueueIndex];
@@ -1065,13 +1065,19 @@ void swift::swift_continuation_logFailedCheck(const char *message) {
   swift_reportError(0, message);
 }
 
+SWIFT_RUNTIME_ATTRIBUTE_NORETURN
 SWIFT_CC(swift)
 static void swift_task_asyncMainDrainQueueImpl() {
 #if SWIFT_CONCURRENCY_COOPERATIVE_GLOBAL_EXECUTOR
   bool Finished = false;
-  donateThreadToGlobalExecutorUntil([](void *context) {
+  swift_task_donateThreadToGlobalExecutorUntil([](void *context) {
     return *reinterpret_cast<bool*>(context);
   }, &Finished);
+#elif !SWIFT_CONCURRENCY_ENABLE_DISPATCH
+  // FIXME: consider implementing a concurrent global main queue for
+  // these environments?
+  swift_reportError(0, "operation unsupported without libdispatch: "
+                       "swift_task_asyncMainDrainQueue");
 #else
 #if defined(_WIN32)
   static void(FAR *pfndispatch_main)(void) = NULL;

stdlib/public/Concurrency/TaskGroup.cpp

@@ -34,7 +34,7 @@
 #include "queue" // TODO: remove and replace with usage of our mpsc queue
 #include <atomic>
 #include <assert.h>
-#if !SWIFT_CONCURRENCY_COOPERATIVE_GLOBAL_EXECUTOR
+#if SWIFT_CONCURRENCY_ENABLE_DISPATCH
 #include <dispatch/dispatch.h>
 #endif
 

stdlib/public/Concurrency/TaskPrivate.h

@@ -100,20 +100,6 @@ void asyncLet_addImpl(AsyncTask *task, AsyncLet *asyncLet,
 /// Clear the active task reference for the current thread.
 AsyncTask *_swift_task_clearCurrent();
 
-#if defined(SWIFT_STDLIB_SINGLE_THREADED_RUNTIME)
-#define SWIFT_CONCURRENCY_COOPERATIVE_GLOBAL_EXECUTOR 1
-#else
-#define SWIFT_CONCURRENCY_COOPERATIVE_GLOBAL_EXECUTOR 0
-#endif
-
-#if SWIFT_CONCURRENCY_COOPERATIVE_GLOBAL_EXECUTOR
-/// Donate this thread to the global executor until either the
-/// given condition returns true or we've run out of cooperative
-/// tasks to run.
-void donateThreadToGlobalExecutorUntil(bool (*condition)(void*),
-                                       void *context);
-#endif
-
 /// release() establishes a happens-before relation with a preceding acquire()
 /// on the same address.
 void _swift_tsan_acquire(void *addr);