[6.3] Fix worker thread name handling on Linux

CMakeLists.txt

@@ -197,7 +197,6 @@ check_function_exists(pthread_attr_setcpupercent_np HAVE_PTHREAD_ATTR_SETCPUPERC
 check_function_exists(pthread_yield_np HAVE_PTHREAD_YIELD_NP)
 check_function_exists(pthread_main_np HAVE_PTHREAD_MAIN_NP)
 check_function_exists(pthread_workqueue_setdispatch_np HAVE_PTHREAD_WORKQUEUE_SETDISPATCH_NP)
-check_function_exists(pthread_setname_np HAVE_PTHREAD_SETNAME_NP)
 check_function_exists(strlcpy HAVE_STRLCPY)
 check_function_exists(sysconf HAVE_SYSCONF)
 check_function_exists(arc4random HAVE_ARC4RANDOM)
@@ -270,6 +269,14 @@ if (HAVE_DECL_PROGRAM_INVOCATION_SHORT_NAME)
   add_compile_definitions($<$<COMPILE_LANGUAGE:C,CXX>:_GNU_SOURCE=1>)
 endif()
 check_symbol_exists(__printflike "bsd/sys/cdefs.h" HAVE_PRINTFLIKE)
+if(UNIX)
+  list(APPEND CMAKE_REQUIRED_LIBRARIES Threads::Threads)
+  check_symbol_exists(pthread_setname_np "pthread.h;pthread_np.h" HAVE_PTHREAD_SETNAME_NP)
+  check_symbol_exists(pthread_getname_np "pthread.h;pthread_np.h" HAVE_PTHREAD_GETNAME_NP)
+  check_symbol_exists(pthread_get_name_np "pthread.h;pthread_np.h" HAVE_PTHREAD_GET_NAME_NP)
+  check_symbol_exists(pthread_set_name_np "pthread.h;pthread_np.h" HAVE_PTHREAD_SET_NAME_NP)
+  list(REMOVE_ITEM CMAKE_REQUIRED_LIBRARIES Threads::Threads)
+endif()
 
 if(ANDROID)
   set(ENABLE_DTRACE_DEFAULT OFF)

cmake/config.h.in

@@ -211,6 +211,15 @@
 /* Define to 1 if you have the `pthread_setname_np' function. */
 #cmakedefine01 HAVE_PTHREAD_SETNAME_NP
 
+/* Define to 1 if you have the `pthread_getname_np' function. */
+#cmakedefine01 HAVE_PTHREAD_GETNAME_NP
+
+/* Define to 1 if you have the `pthread_set_name_np' function. */
+#cmakedefine01 HAVE_PTHREAD_SET_NAME_NP
+
+/* Define to 1 if you have the `pthread_get_name_np' function. */
+#cmakedefine01 HAVE_PTHREAD_GET_NAME_NP
+
 /* Define to use non-portable pthread TSD optimizations for Mac OS X) */
 #cmakedefine USE_APPLE_TSD_OPTIMIZATIONS
 

src/queue.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Apple Inc. All rights reserved.
+ * Copyright (c) 2008-2026 Apple Inc. All rights reserved.
  *
  * @APPLE_APACHE_LICENSE_HEADER_START@
  *
@@ -6246,6 +6246,12 @@ _dispatch_worker_thread(void *context)
 	dispatch_priority_t pri = dq->dq_priority;
 	pthread_priority_t pp = _dispatch_get_priority();
 
+	#if HAVE_PTHREAD_SETNAME_NP
+	pthread_setname_np(pthread_self(), "DispatchWorker");
+	#elif HAVE_PTHREAD_SET_NAME_NP
+	pthread_set_name_np(pthread_self(), "DispatchWorker");
+	#endif // HAVE_PTHREAD_SETNAME_NP
+
 #if defined(__linux__)
 	// The Linux kernel does not have a direct analogue to the QoS-based
 	// thread policy engine found in XNU.
@@ -6263,21 +6269,6 @@ _dispatch_worker_thread(void *context)
 	pp = _dispatch_priority_to_pp_strip_flags(pri);
 	int nice = _dispatch_pp_to_nice(pp);
 
-	#if HAVE_PTHREAD_SETNAME_NP 
-	// pthread thread names are restricted to just 16 characters
-	// including NUL. Truncate the label name from the beginning as it tends 
-	// to be more unique at the end.
-	size_t label_length = strlen(dq->dq_label); 
-	const char * thread_name = dq->dq_label;
-	if (label_length > 0) { 
-		const size_t max_thread_name_length = 16 - 1;  // minus the NUL byte; 
-		thread_name = thread_name + (label_length - max_thread_name_length); 
-	} else { 
-		thread_name = "DispatchWorker";
-	}
-	pthread_setname_np(pthread_self(), thread_name);
-	#endif // HAVE_PTHREAD_SETNAME_NP
-
 	errno = 0;
 	int rc = setpriority(PRIO_PROCESS, 0, nice);
 	if (rc != -1 || errno == 0) {

tests/CMakeLists.txt

@@ -163,6 +163,10 @@ if(EXTENDED_TEST_SUITE)
 endif()
 
 # add C tests for platform-specific functionality when applicable
+if(UNIX AND (HAVE_PTHREAD_SETNAME_NP OR HAVE_PTHREAD_SET_NAME_NP))
+  list(APPEND DISPATCH_C_TESTS
+       thread_name)
+endif()
 if(APPLE)
   list(APPEND DISPATCH_C_TESTS
        deadname

tests/dispatch_thread_name.c

@@ -0,0 +1,88 @@
+/*
+ * Copyright (c) 2026 Apple Inc. All rights reserved.
+ *
+ * @APPLE_APACHE_LICENSE_HEADER_START@
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * @APPLE_APACHE_LICENSE_HEADER_END@
+ */
+
+#include <dispatch/dispatch.h>
+#include <stdio.h>
+#include <string.h>
+#include <assert.h>
+
+#if defined(__unix__) || (defined(__APPLE__) && defined(__MACH__))
+#include <pthread.h>
+#include <unistd.h>
+#endif
+#if defined(__OpenBSD__) || defined(__FreeBSD__)
+#include <pthread_np.h>
+#endif
+
+#include <bsdtests.h>
+
+#if HAVE_PTHREAD_SET_NAME_NP && !HAVE_PTHREAD_SETNAME_NP
+#define pthread_setname_np pthread_set_name_np
+#endif
+#if HAVE_PTHREAD_GET_NAME_NP && !HAVE_PTHREAD_GETNAME_NP
+#define pthread_getname_np pthread_get_name_np
+#endif
+
+#include <bsdtests.h>
+#include "dispatch_test.h"
+
+#define ITERATIONS 10
+
+static void
+set_current_thread_name(const char *name)
+{
+#if defined(__APPLE__)
+	pthread_setname_np(name);
+#else
+	pthread_setname_np(pthread_self(), name);
+#endif
+}
+
+int
+main(void)
+{
+	dispatch_test_start("Dispatch Thread Name");
+
+	const char *parent_name = "TestParentName";
+	set_current_thread_name(parent_name);
+
+	dispatch_group_t group = dispatch_group_create();
+	assert(group);
+
+	dispatch_queue_t q = dispatch_get_global_queue(0, 0);
+
+	for (int i = 0; i < ITERATIONS; i++) {
+		dispatch_group_async(group, q, ^{
+			char thread_name[64] = {0};
+			pthread_getname_np(pthread_self(), thread_name, sizeof(thread_name));
+			fprintf(stderr, "Worker thread name: '%s'\n", thread_name);
+			test_long("worker thread name must not be empty",
+					strlen(thread_name) > 0, 1);
+			test_long("worker thread must not inherit parent name",
+					strcmp(thread_name, parent_name) != 0, 1);
+		});
+	}
+
+	test_group_wait(group);
+	dispatch_release(group);
+
+	test_stop();
+	return 0;
+}