Add a build option for the concurrency tracing feature.

stdlib/cmake/modules/AddSwiftStdlib.cmake

@@ -373,11 +373,15 @@ function(_add_target_variant_c_compile_flags)
   if(SWIFT_STDLIB_SUPPORTS_BACKTRACE_REPORTING)
     list(APPEND result "-DSWIFT_STDLIB_SUPPORTS_BACKTRACE_REPORTING")
   endif()
-  
+
   if(SWIFT_STDLIB_ENABLE_UNICODE_DATA)
     list(APPEND result "-D" "SWIFT_STDLIB_ENABLE_UNICODE_DATA")
   endif()
 
+  if(SWIFT_STDLIB_CONCURRENCY_TRACING)
+    list(APPEND result "-DSWIFT_STDLIB_CONCURRENCY_TRACING")
+  endif()
+
   list(APPEND result ${SWIFT_STDLIB_EXTRA_C_COMPILE_FLAGS})
 
   set("${CFLAGS_RESULT_VAR_NAME}" "${result}" PARENT_SCOPE)

stdlib/cmake/modules/StdlibOptions.cmake

@@ -183,3 +183,14 @@ option(SWIFT_FREESTANDING_FLAVOR
 set(SWIFT_STDLIB_ENABLE_LTO OFF CACHE STRING "Build Swift stdlib with LTO. One
     must specify the form of LTO by setting this to one of: 'full', 'thin'. This
     option only affects the standard library and runtime, not tools.")
+
+if("${SWIFT_HOST_VARIANT_SDK}" IN_LIST SWIFT_DARWIN_PLATFORMS)
+  set(SWIFT_STDLIB_CONCURRENCY_TRACING_default TRUE)
+else()
+  set(SWIFT_STDLIB_CONCURRENCY_TRACING_default FALSE)
+endif()
+
+option(SWIFT_STDLIB_CONCURRENCY_TRACING
+  "Enable concurrency tracing in the runtime; assumes the presence of os_log(3)
+   and the os_signpost(3) API."
+  "${SWIFT_STDLIB_CONCURRENCY_TRACING_default}")

stdlib/public/Concurrency/Tracing.h

@@ -96,7 +96,7 @@ void job_run_end(ExecutorRef *executor, job_run_info info);
 } // namespace concurrency
 } // namespace swift
 
-#if __has_include(<os/signpost.h>)
+#if SWIFT_STDLIB_CONCURRENCY_TRACING
 #include "TracingSignpost.h"
 #else
 #include "TracingStubs.h"

stdlib/public/Concurrency/TracingSignpost.cpp

@@ -14,7 +14,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if __has_include(<os/signpost.h>)
+#if SWIFT_STDLIB_CONCURRENCY_TRACING
 
 #include "TracingSignpost.h"
 #include <stdio.h>

utils/build-presets.ini

@@ -2528,6 +2528,7 @@ swift-stdlib-has-environ=0
 swift-stdlib-has-locale=0
 swift-runtime-static-image-inspection=1
 swift-stdlib-single-threaded-runtime=1
+swift-stdlib-concurrency-tracing=0
 swift-stdlib-os-versioning=0
 swift-stdlib-has-commandline=0
 swift-stdlib-lto=full

utils/build-script-impl

@@ -206,6 +206,7 @@ KNOWN_SETTINGS=(
     swift-stdlib-supports-backtrace-reporting     ""                "whether to build stdlib assuming the runtime environment provides the backtrace(3) API, if not set defaults to true on all platforms except for Cygwin, Haiku and wasm"
     swift-runtime-static-image-inspection         "0"               "whether to build stdlib assuming the runtime environment only supports a single runtime image with Swift code"
     swift-stdlib-single-threaded-runtime          "0"               "whether to build stdlib as a single-threaded runtime only"
+    swift-stdlib-concurrency-tracing              ""                "whether to enable tracing signposts for concurrency; default is 1 on Darwin platforms, 0 otherwise"
     swift-stdlib-os-versioning                    "1"               "whether to build stdlib with availability based on OS versions (Darwin only)"
     swift-stdlib-has-commandline                  "1"               "whether to build stdlib with the CommandLine enum and support for argv/argc"
     swift-stdlib-stable-abi                       ""                "should stdlib be built with stable ABI, if not set defaults to true on Darwin, false otherwise"
@@ -2210,6 +2211,13 @@ for host in "${ALL_HOSTS[@]}"; do
                     )
                 fi
 
+                if [[ "${SWIFT_STDLIB_CONCURRENCY_TRACING}" ]] ; then
+                    cmake_options=(
+                        "${cmake_options[@]}"
+                        -DSWIFT_STDLIB_CONCURRENCY_TRACING:BOOL=$(true_false "${SWIFT_STDLIB_CONCURRENCY_TRACING}")
+                    )
+                fi
+
                 build_targets=(all "${SWIFT_STDLIB_TARGETS[@]}")
                 if [[ $(true_false "${build_perf_testsuite_this_time}") == "TRUE" ]]; then
                     native_swift_tools_path="$(build_directory_bin ${LOCAL_HOST} swift)"