[Qemu-devel] [PATCH v2 2/7] qemu-thread: add per-thread atexit functions

[Paolo Bonzini]

Destructors are the main additional feature of pthread TLS compared
to __thread.  If we were using C++ (hint, hint!) we could have used
thread-local objects with a destructor.  Since we are not, instead,
we add a simple Notifier-based API.

Note that the notifier must be per-thread as well.  We can add a
global list as well later, perhaps.

The Win32 implementation has some complications because a) detached
threads used not to have a QemuThreadData; b) the main thread does
not go through win32_start_routine, so we have to use atexit too.

Signed-off-by: Paolo Bonzini <address@hidden>
---
v1->v2: rename run_main_iothread_exit -> run_main_thread_exit

 include/qemu/thread.h    |  4 ++++
 util/qemu-thread-posix.c | 37 +++++++++++++++++++++++++++++++++++++
 util/qemu-thread-win32.c | 48 +++++++++++++++++++++++++++++++++++++-----------
 3 files changed, 78 insertions(+), 11 deletions(-)

diff --git a/include/qemu/thread.h b/include/qemu/thread.h
index f7e3b9b..e89fdc9 100644
--- a/include/qemu/thread.h
+++ b/include/qemu/thread.h
@@ -61,4 +61,8 @@ bool qemu_thread_is_self(QemuThread *thread);
 void qemu_thread_exit(void *retval);
 void qemu_thread_naming(bool enable);
 
+struct Notifier;
+void qemu_thread_atexit_add(struct Notifier *notifier);
+void qemu_thread_atexit_remove(struct Notifier *notifier);
+
 #endif
diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c
index d05a649..41cb23d 100644
--- a/util/qemu-thread-posix.c
+++ b/util/qemu-thread-posix.c
@@ -26,6 +26,7 @@
 #endif
 #include "qemu/thread.h"
 #include "qemu/atomic.h"
+#include "qemu/notify.h"
 
 static bool name_threads;
 
@@ -401,6 +402,42 @@ void qemu_event_wait(QemuEvent *ev)
     }
 }
 
+static pthread_key_t exit_key;
+
+union NotifierThreadData {
+    void *ptr;
+    NotifierList list;
+};
+QEMU_BUILD_BUG_ON(sizeof(union NotifierThreadData) != sizeof(void *));
+
+void qemu_thread_atexit_add(Notifier *notifier)
+{
+    union NotifierThreadData ntd;
+    ntd.ptr = pthread_getspecific(exit_key);
+    notifier_list_add(&ntd.list, notifier);
+    pthread_setspecific(exit_key, ntd.ptr);
+}
+
+void qemu_thread_atexit_remove(Notifier *notifier)
+{
+    union NotifierThreadData ntd;
+    ntd.ptr = pthread_getspecific(exit_key);
+    notifier_remove(notifier);
+    pthread_setspecific(exit_key, ntd.ptr);
+}
+
+static void qemu_thread_atexit_run(void *arg)
+{
+    union NotifierThreadData ntd = { .ptr = arg };
+    notifier_list_notify(&ntd.list, NULL);
+}
+
+static void __attribute__((constructor)) qemu_thread_atexit_init(void)
+{
+    pthread_key_create(&exit_key, qemu_thread_atexit_run);
+}
+
+
 /* Attempt to set the threads name; note that this is for debug, so
  * we're not going to fail if we can't set it.
  */
diff --git a/util/qemu-thread-win32.c b/util/qemu-thread-win32.c
index c405c9b..7bda85b 100644
--- a/util/qemu-thread-win32.c
+++ b/util/qemu-thread-win32.c
@@ -12,6 +12,7 @@
  */
 #include "qemu-common.h"
 #include "qemu/thread.h"
+#include "qemu/notify.h"
 #include <process.h>
 #include <assert.h>
 #include <limits.h>
@@ -268,6 +269,7 @@ struct QemuThreadData {
     void             *(*start_routine)(void *);
     void             *arg;
     short             mode;
+    NotifierList      exit;
 
     /* Only used for joinable threads. */
     bool              exited;
@@ -275,18 +277,40 @@ struct QemuThreadData {
     CRITICAL_SECTION  cs;
 };
 
+static bool atexit_registered;
+static NotifierList main_thread_exit;
+
 static __thread QemuThreadData *qemu_thread_data;
 
+static void run_main_thread_exit(void)
+{
+    notifier_list_notify(&main_thread_exit, NULL);
+}
+
+void qemu_thread_atexit_add(Notifier *notifier)
+{
+    if (!qemu_thread_data) {
+        if (!atexit_registered) {
+            atexit_registered = true;
+            atexit(run_main_thread_exit);
+        }
+        notifier_list_add(&main_thread_exit, notifier);
+    } else {
+        notifier_list_add(&qemu_thread_data->exit, notifier);
+    }
+}
+
+void qemu_thread_atexit_remove(Notifier *notifier)
+{
+    notifier_remove(notifier);
+}
+
 static unsigned __stdcall win32_start_routine(void *arg)
 {
     QemuThreadData *data = (QemuThreadData *) arg;
     void *(*start_routine)(void *) = data->start_routine;
     void *thread_arg = data->arg;
 
-    if (data->mode == QEMU_THREAD_DETACHED) {
-        g_free(data);
-        data = NULL;
-    }
     qemu_thread_data = data;
     qemu_thread_exit(start_routine(thread_arg));
     abort();
@@ -296,12 +320,14 @@ void qemu_thread_exit(void *arg)
 {
     QemuThreadData *data = qemu_thread_data;
 
-    if (data) {
-        assert(data->mode != QEMU_THREAD_DETACHED);
+    notifier_list_notify(&data->exit, NULL);
+    if (data->mode == QEMU_THREAD_JOINABLE) {
         data->ret = arg;
         EnterCriticalSection(&data->cs);
         data->exited = true;
         LeaveCriticalSection(&data->cs);
+    } else {
+        g_free(data);
     }
     _endthreadex(0);
 }
@@ -313,9 +339,10 @@ void *qemu_thread_join(QemuThread *thread)
     HANDLE handle;
 
     data = thread->data;
-    if (!data) {
+    if (data->mode == QEMU_THREAD_DETACHED) {
         return NULL;
     }
+
     /*
      * Because multiple copies of the QemuThread can exist via
      * qemu_thread_get_self, we need to store a value that cannot
@@ -329,7 +356,6 @@ void *qemu_thread_join(QemuThread *thread)
         CloseHandle(handle);
     }
     ret = data->ret;
-    assert(data->mode != QEMU_THREAD_DETACHED);
     DeleteCriticalSection(&data->cs);
     g_free(data);
     return ret;
@@ -347,6 +373,7 @@ void qemu_thread_create(QemuThread *thread, const char 
*name,
     data->arg = arg;
     data->mode = mode;
     data->exited = false;
+    notifier_list_init(&data->exit);
 
     if (data->mode != QEMU_THREAD_DETACHED) {
         InitializeCriticalSection(&data->cs);
@@ -358,7 +385,7 @@ void qemu_thread_create(QemuThread *thread, const char 
*name,
         error_exit(GetLastError(), __func__);
     }
     CloseHandle(hThread);
-    thread->data = (mode == QEMU_THREAD_DETACHED) ? NULL : data;
+    thread->data = data;
 }
 
 void qemu_thread_get_self(QemuThread *thread)
@@ -373,11 +400,10 @@ HANDLE qemu_thread_get_handle(QemuThread *thread)
     HANDLE handle;
 
     data = thread->data;
-    if (!data) {
+    if (data->mode == QEMU_THREAD_DETACHED) {
         return NULL;
     }
 
-    assert(data->mode != QEMU_THREAD_DETACHED);
     EnterCriticalSection(&data->cs);
     if (!data->exited) {
         handle = OpenThread(SYNCHRONIZE | THREAD_SUSPEND_RESUME, FALSE,
-- 
2.1.0