util: add API to fetch the current thread name
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 when it is called repeatedly in a single thread. The thread name should be set at the very start of the thread execution, which is the case when using qemu_thread_create. This uses the official thread APIs for fetching thread names, so that it captures names of threads spawned by code in 3rd party libraries, not merely QEMU spawned thrads. This also addresses the gap from the previous patch for setting the name of the main thread. A constructor is used to initialize the 'namebuf' thread-local in the main thread only. Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Daniel P. Berrangé committed
Aug 29, 2025 at 16:30 UTC
215235d365e49c72a85ea2940751e45419676031
4 files changed
+119
-5
include/qemu/thread.h
+1
@@ -216,6 +216,7 @@ void qemu_thread_get_self(QemuThread *thread);
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bool qemu_thread_is_self(QemuThread *thread);
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G_NORETURN void qemu_thread_exit(void *retval);
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void qemu_thread_set_name(const char *name);
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+const char *qemu_thread_get_name(void);
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struct Notifier;
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/**
meson.build
+21
@@ -2856,6 +2856,27 @@ config_host_data.set('CONFIG_PTHREAD_SET_NAME_NP', cc.links(osdep_prefix + '''
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pthread_set_name_np(thread, "QEMU");
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return 0;
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}''', dependencies: threads))
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+
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+config_host_data.set('CONFIG_PTHREAD_GETNAME_NP', cc.links(osdep_prefix + '''
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+ #include <pthread.h>
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+
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+ int main(void)
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+ {
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+ char buf[16];
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+ pthread_getname_np(pthread_self(), buf, sizeof(buf));
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+ return 0;
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+ }''', dependencies: threads))
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+config_host_data.set('CONFIG_PTHREAD_GET_NAME_NP', cc.links(osdep_prefix + '''
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+ #include <pthread.h>
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+ #include <pthread_np.h>
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+
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+ int main(void)
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+ {
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+ char buf[16];
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+ pthread_get_name_np(pthread_self(), buf, sizeof(buf));
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+ return 0;
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+ }''', dependencies: threads))
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+
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config_host_data.set('CONFIG_PTHREAD_CONDATTR_SETCLOCK', cc.links(osdep_prefix + '''
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#include <pthread.h>
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util/qemu-thread-posix.c
+52
-1
@@ -18,10 +18,41 @@
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#include "qemu/tsan.h"
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#include "qemu/bitmap.h"
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-#ifdef CONFIG_PTHREAD_SET_NAME_NP
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+#if defined(CONFIG_PTHREAD_SET_NAME_NP) || defined(CONFIG_PTHREAD_GET_NAME_NP)
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#include <pthread_np.h>
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#endif
24
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+/*
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+ * This is not defined on Linux, but the man page indicates
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+ * the buffer must be at least 16 bytes, including the NUL
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+ * terminator
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+ */
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+#ifndef PTHREAD_MAX_NAMELEN_NP
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+#define PTHREAD_MAX_NAMELEN_NP 16
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+#endif
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+
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+static __thread char namebuf[PTHREAD_MAX_NAMELEN_NP];
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+
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+static void __attribute__((__constructor__(QEMU_CONSTRUCTOR_EARLY)))
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+qemu_thread_init(void)
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+{
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+ /*
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+ * Initialize the main thread name. We must not use
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+ * qemu_thread_setname(), since on some platforms (at least Linux)
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+ * this can change the process name that is reported by tools like
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+ * 'ps'.
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+ *
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+ * This workaround suffices to ensure QEMU log/error messages
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+ * get the main thread name, but at the cost of external tools
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+ * like GDB not seeing it.
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+ *
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+ * NB using a constructor instead of static initializing namebuf,
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+ * to ensure it only initializes the thread-local in the main
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+ * thread
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+ */
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+ g_strlcpy(namebuf, "main", sizeof(namebuf));
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+}
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+
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static void error_exit(int err, const char *msg)
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{
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fprintf(stderr, "qemu: %s: %s\n", msg, strerror(err));
@@ -526,3 +557,23 @@ void *qemu_thread_join(QemuThread *thread)
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}
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return ret;
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}
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+
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+const char *qemu_thread_get_name(void)
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+{
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+ int rv;
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+ if (namebuf[0] != '\0') {
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+ return namebuf;
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+ }
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+
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+# if defined(CONFIG_PTHREAD_GETNAME_NP)
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+ rv = pthread_getname_np(pthread_self(), namebuf, sizeof(namebuf));
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+# elif defined(CONFIG_PTHREAD_GET_NAME_NP)
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+ rv = pthread_get_name_np(pthread_self(), namebuf, sizeof(namebuf));
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+# else
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+ rv = -1;
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+# endif
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+ if (rv != 0) {
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+ g_strlcpy(namebuf, "unnamed", G_N_ELEMENTS(namebuf));
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+ }
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+ return namebuf;
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+}
util/qemu-thread-win32.c
+45
-4
@@ -19,7 +19,10 @@
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typedef HRESULT (WINAPI *pSetThreadDescription) (HANDLE hThread,
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PCWSTR lpThreadDescription);
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+typedef HRESULT (WINAPI *pGetThreadDescription) (HANDLE hThread,
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+ PWSTR *lpThreadDescription);
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static pSetThreadDescription SetThreadDescriptionFunc;
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+static pGetThreadDescription GetThreadDescriptionFunc;
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static HMODULE kernel32_module;
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static void __attribute__((__constructor__(QEMU_CONSTRUCTOR_EARLY)))
@@ -28,7 +31,7 @@ qemu_thread_init(void)
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qemu_thread_set_name("main");
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}
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-static bool load_set_thread_description(void)
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+static bool load_thread_description(void)
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{
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static gsize _init_once = 0;
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@@ -38,14 +41,17 @@ static bool load_set_thread_description(void)
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SetThreadDescriptionFunc =
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(pSetThreadDescription)GetProcAddress(kernel32_module,
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"SetThreadDescription");
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- if (!SetThreadDescriptionFunc) {
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+ GetThreadDescriptionFunc =
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+ (pGetThreadDescription)GetProcAddress(kernel32_module,
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+ "GetThreadDescription");
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+ if (!SetThreadDescriptionFunc || !GetThreadDescriptionFunc) {
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FreeLibrary(kernel32_module);
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}
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}
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g_once_init_leave(&_init_once, 1);
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}
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48
- return !!SetThreadDescriptionFunc;
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+ return (SetThreadDescriptionFunc && GetThreadDescriptionFunc);
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}
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static void error_exit(int err, const char *msg)
@@ -331,7 +337,7 @@ void qemu_thread_set_name(const char *name)
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{
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g_autofree wchar_t *namew = NULL;
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- if (!load_set_thread_description()) {
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+ if (!load_thread_description()) {
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return;
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}
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@@ -415,3 +421,38 @@ bool qemu_thread_is_self(QemuThread *thread)
421
{
422
return GetCurrentThreadId() == thread->tid;
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}
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+
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+static __thread char namebuf[64];
426
+
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+const char *qemu_thread_get_name(void)
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+{
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+ HRESULT hr;
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+ wchar_t *namew = NULL;
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+ g_autofree char *name = NULL;
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+
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+ if (namebuf[0] != '\0') {
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+ return namebuf;
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+ }
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+
437
+ if (!load_thread_description()) {
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+ goto error;
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+ }
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+
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+ hr = GetThreadDescriptionFunc(GetCurrentThread(), &namew);
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+ if (!SUCCEEDED(hr)) {
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+ goto error;
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+ }
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+
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+ name = g_utf16_to_utf8(namew, -1, NULL, NULL, NULL);
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+ LocalFree(namew);
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+ if (!name) {
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+ goto error;
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+ }
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+
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+ g_strlcpy(namebuf, name, G_N_ELEMENTS(namebuf));
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+ return namebuf;
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+
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+ error:
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+ g_strlcpy(namebuf, "unnamed", G_N_ELEMENTS(namebuf));
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+ return namebuf;
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+}