Stop using SWIFT_STDLIB_SINGLE_THREADED_CONCURRENCY under SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY (#62735)

Using single-threaded concurrency was a temporary solution, now that the task-to-thread model actually supports multiple threads, let's switch off of it. Instead, let's introduce a "global executor none" option (implicitly set under the task-to-thread model) to denote that the concurrency model is not using a global executor.

rdar://99448771

include/swift/Runtime/DispatchShims.h

@@ -18,6 +18,10 @@
 #if SWIFT_CONCURRENCY_ENABLE_PRIORITY_ESCALATION
 #include <dispatch/swift_concurrency_private.h>
 
+#if SWIFT_CONCURRENCY_TASK_TO_THREAD_MODEL
+#error Cannot use task-to-thread model with priority escalation
+#endif
+
 // Provide wrappers with runtime checks to make sure that the dispatch functions
 // are only called on OS-es where they are supported
 static inline dispatch_thread_override_info_s

include/swift/Runtime/VoucherShims.h

@@ -40,6 +40,10 @@
 
 #if SWIFT_HAS_VOUCHERS
 
+#if SWIFT_CONCURRENCY_TASK_TO_THREAD_MODEL
+#error Cannot use task-to-thread model with vouchers
+#endif
+
 #if SWIFT_HAS_VOUCHER_HEADER
 
 #else

stdlib/CMakeLists.txt

@@ -180,6 +180,19 @@ if("${SWIFT_CONCURRENCY_GLOBAL_EXECUTOR}" STREQUAL "singlethreaded"
   message(SEND_ERROR "Cannot enable the single-threaded global executor without enabling SWIFT_STDLIB_SINGLE_THREADED_CONCURRENCY")
 endif()
 
+if(SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY)
+  if(SWIFT_STDLIB_SINGLE_THREADED_CONCURRENCY)
+    message(SEND_ERROR "Cannot use the single-threaded concurrency with task-to-thread concurrency model")
+  endif()
+  if(NOT "${SWIFT_CONCURRENCY_GLOBAL_EXECUTOR}" STREQUAL "none")
+    message(SEND_ERROR "Task-to-thread concurrency model requires no global executor")
+  endif()
+else()
+  if("${SWIFT_CONCURRENCY_GLOBAL_EXECUTOR}" STREQUAL "none")
+    message(SEND_ERROR "Only task-to-thread concurrency model is usable with no global executor")
+  endif()
+endif()
+
 swift_create_stdlib_targets("swift-stdlib" "" TRUE)
 if(SWIFT_STDLIB_ENABLE_SIB_TARGETS)
   swift_create_stdlib_targets("swift-stdlib" "sib" TRUE)

stdlib/cmake/modules/StdlibOptions.cmake

@@ -197,7 +197,9 @@ option(SWIFT_STDLIB_SINGLE_THREADED_CONCURRENCY
        "Build the standard libraries assuming that they will be used in an environment with only a single thread."
        FALSE)
 
-if(SWIFT_STDLIB_SINGLE_THREADED_CONCURRENCY)
+if(SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY)
+  set(SWIFT_CONCURRENCY_GLOBAL_EXECUTOR_default "none")
+elseif(SWIFT_STDLIB_SINGLE_THREADED_CONCURRENCY)
   set(SWIFT_CONCURRENCY_GLOBAL_EXECUTOR_default "singlethreaded")
 else()
   set(SWIFT_CONCURRENCY_GLOBAL_EXECUTOR_default "dispatch")
@@ -205,7 +207,7 @@ endif()
 
 set(SWIFT_CONCURRENCY_GLOBAL_EXECUTOR
     "${SWIFT_CONCURRENCY_GLOBAL_EXECUTOR_default}" CACHE STRING
-    "Build the concurrency library to use the given global executor (options: dispatch, singlethreaded, hooked)")
+    "Build the concurrency library to use the given global executor (options: none, dispatch, singlethreaded, hooked)")
 
 option(SWIFT_STDLIB_OS_VERSIONING
        "Build stdlib with availability based on OS versions (Darwin only)."

stdlib/public/Concurrency/Actor.cpp

@@ -283,6 +283,8 @@ static bool isExecutingOnMainThread() {
 JobPriority swift::swift_task_getCurrentThreadPriority() {
 #if SWIFT_STDLIB_SINGLE_THREADED_CONCURRENCY
   return JobPriority::UserInitiated;
+#elif SWIFT_CONCURRENCY_TASK_TO_THREAD_MODEL
+  return JobPriority::Unspecified;
 #elif defined(__APPLE__)
   return static_cast<JobPriority>(qos_class_self());
 #else

stdlib/public/Concurrency/CMakeLists.txt

@@ -44,7 +44,8 @@ if("${SWIFT_CONCURRENCY_GLOBAL_EXECUTOR}" STREQUAL "dispatch")
       dispatch)
   endif()
 elseif("${SWIFT_CONCURRENCY_GLOBAL_EXECUTOR}" STREQUAL "singlethreaded" OR
-       "${SWIFT_CONCURRENCY_GLOBAL_EXECUTOR}" STREQUAL "hooked")
+       "${SWIFT_CONCURRENCY_GLOBAL_EXECUTOR}" STREQUAL "hooked" OR
+       "${SWIFT_CONCURRENCY_GLOBAL_EXECUTOR}" STREQUAL "none")
   list(APPEND SWIFT_RUNTIME_CONCURRENCY_C_FLAGS
     "-DSWIFT_CONCURRENCY_ENABLE_DISPATCH=0")
 else()

test/Concurrency/Runtime/cancellation_handler.swift

@@ -5,7 +5,7 @@
 // rdar://76038845
 // REQUIRES: concurrency_runtime
 // UNSUPPORTED: back_deployment_runtime
-// UNSUPPORTED: single_threaded_concurrency
+// UNSUPPORTED: freestanding
 
 // for sleep
 #if canImport(Darwin)

utils/build-presets.ini

@@ -2544,7 +2544,6 @@ swift-stdlib-has-stdin=0
 swift-stdlib-has-environ=0
 swift-stdlib-has-locale=0
 swift-runtime-static-image-inspection=1
-swift-stdlib-single-threaded-concurrency=1
 swift-stdlib-concurrency-tracing=0
 swift-stdlib-os-versioning=0
 swift-stdlib-has-commandline=0