[PATCH 06/12] util: add API to fetch the current thread name

19 Aug 2025

This will be used to include the thread name in error reports
in a later patch. It returns a const string stored in a thread
local to avoid memory allocation on POSIX platforms, at the
cost of having to store an allocated string pointer on Windows.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 include/qemu/thread.h    |  1 +
 meson.build              | 21 +++++++++++++++++
 util/qemu-thread-posix.c | 25 +++++++++++++++++++-
 util/qemu-thread-win32.c | 50 ++++++++++++++++++++++++++++++++++++----
 4 files changed, 92 insertions(+), 5 deletions(-)

diff --git a/include/qemu/thread.h b/include/qemu/thread.h
index 96eee82679..0366cb743d 100644
--- a/include/qemu/thread.h
+++ b/include/qemu/thread.h
@@ -216,6 +216,7 @@ void qemu_thread_get_self(QemuThread *thread);
 bool qemu_thread_is_self(QemuThread *thread);
 G_NORETURN void qemu_thread_exit(void *retval);
 uint64_t qemu_thread_get_id(void);
+const char *qemu_thread_get_name(void);
 
 struct Notifier;
 /**
diff --git a/meson.build b/meson.build
index 50c774a195..ebdcb5d65d 100644
--- a/meson.build
+++ b/meson.build
@@ -2920,6 +2920,27 @@ config_host_data.set('CONFIG_PTHREAD_SET_NAME_NP', cc.links(osdep_prefix + '''
     pthread_set_name_np(thread, "QEMU");
     return 0;
   }''', dependencies: threads))
+
+config_host_data.set('CONFIG_PTHREAD_GETNAME_NP', cc.links(osdep_prefix + '''
+  #include <pthread.h>
+
+  int main(void)
+  {
+    char buf[16];
+    pthread_getname_np(pthread_self(), buf, sizeof(buf));
+    return 0;
+  }''', dependencies: threads))
+config_host_data.set('CONFIG_PTHREAD_GET_NAME_NP', cc.links(osdep_prefix + '''
+  #include <pthread.h>
+  #include <pthread_np.h>
+
+  int main(void)
+  {
+    char buf[16];
+    pthread_get_name_np(pthread_self(), buf, sizeof(buf));
+    return 0;
+  }''', dependencies: threads))
+
 config_host_data.set('CONFIG_PTHREAD_CONDATTR_SETCLOCK', cc.links(osdep_prefix + '''
   #include <pthread.h>
 
diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c
index f240a93632..282802bc39 100644
--- a/util/qemu-thread-posix.c
+++ b/util/qemu-thread-posix.c
@@ -18,7 +18,7 @@
 #include "qemu/tsan.h"
 #include "qemu/bitmap.h"
 
-#ifdef CONFIG_PTHREAD_SET_NAME_NP
+#if defined(CONFIG_PTHREAD_SET_NAME_NP) || defined(CONFIG_PTHREAD_GET_NAME_NP)
 #include <pthread_np.h>
 #endif
 
@@ -543,3 +543,26 @@ uint64_t qemu_thread_get_id(void)
     return (uint64_t)pthread_self();
 #endif
 }
+
+#ifndef PTHREAD_MAX_NAMELEN_NP
+#define PTHREAD_MAX_NAMELEN_NP 16
+#endif
+
+static __thread char namebuf[PTHREAD_MAX_NAMELEN_NP];
+
+const char *qemu_thread_get_name(void)
+{
+    int rv;
+# if defined(CONFIG_PTHREAD_GETNAME_NP)
+    rv = pthread_getname_np(pthread_self(), namebuf, sizeof(namebuf));
+# elif defined(CONFIG_PTHREAD_GET_NAME_NP)
+    rv = pthread_get_name_np(pthread_self(), namebuf, sizeof(namebuf));
+# else
+    rv = -1;
+# endif
+    if (rv != 0) {
+        strncpy(namebuf, "unnamed", sizeof(namebuf) - 1);
+        namebuf[sizeof(namebuf) - 1] = '\0';
+    }
+    return namebuf;
+}
diff --git a/util/qemu-thread-win32.c b/util/qemu-thread-win32.c
index f6956717b2..c31a8a6bc8 100644
--- a/util/qemu-thread-win32.c
+++ b/util/qemu-thread-win32.c
@@ -19,10 +19,13 @@
 
 typedef HRESULT (WINAPI *pSetThreadDescription) (HANDLE hThread,
                                                  PCWSTR lpThreadDescription);
+typedef HRESULT (WINAPI *pGetThreadDescription) (HANDLE hThread,
+                                                 PWSTR *lpThreadDescription);
 static pSetThreadDescription SetThreadDescriptionFunc;
+static pGetThreadDescription GetThreadDescriptionFunc;
 static HMODULE kernel32_module;
 
-static bool load_set_thread_description(void)
+static bool load_thread_description(void)
 {
     static gsize _init_once = 0;
 
@@ -32,14 +35,17 @@ static bool load_set_thread_description(void)
             SetThreadDescriptionFunc =
                 (pSetThreadDescription)GetProcAddress(kernel32_module,
                                                       "SetThreadDescription");
-            if (!SetThreadDescriptionFunc) {
+            GetThreadDescriptionFunc =
+                (pGetThreadDescription)GetProcAddress(kernel32_module,
+                                                      "GetThreadDescription");
+            if (!SetThreadDescriptionFunc || !GetThreadDescriptionFunc) {
                 FreeLibrary(kernel32_module);
             }
         }
         g_once_init_leave(&_init_once, 1);
     }
 
-    return !!SetThreadDescriptionFunc;
+    return !!(SetThreadDescriptionFunc && GetThreadDescriptionFunc);
 }
 
 static void error_exit(int err, const char *msg)
@@ -320,7 +326,7 @@ static void set_thread_description(HANDLE h, const char *name)
 {
     g_autofree wchar_t *namew = NULL;
 
-    if (!load_set_thread_description()) {
+    if (!load_thread_description()) {
         return;
     }
 
@@ -417,3 +423,39 @@ uint64_t qemu_thread_get_id(void)
 {
     return (uint64_t)GetCurrentThreadId();
 }
+
+static __thread char *namebuf;
+
+const char *qemu_thread_get_name(void)
+{
+    HRESULT hr;
+    wchar_t *namew = NULL;
+    g_autofree char *name = NULL;
+
+    if (!load_thread_description()) {
+        goto error;
+    }
+
+    hr = GetThreadDescriptionFunc(GetCurrentThread(), &namew);
+    if (!SUCCEEDED(hr)) {
+        goto error;
+    }
+
+    g_free(namebuf);
+    namebuf = g_utf16_to_utf8(namew, -1, NULL, NULL, NULL);
+    if (!namebuf) {
+        goto error;
+    }
+
+ cleanup:
+    if (namew) {
+        LocalFree(namew);
+    }
+    return namebuf;
+
+ error:
+    if (!namebuf) {
+        namebuf = g_strdup("unnamed");
+    }
+    goto cleanup;
+}
-- 
2.50.1

    