unix,win: add uv_library_shutdown()

Make it possible to explicitly tell libuv to release any resources
it's still holding onto (memory, threads, file descriptors, etc.)

Before this commit, cleanup was performed in various destructors.
This commit centralizes the cleanup logic, enabling the addition of
`uv_library_shutdown()`, but maintains the current observable behavior
of cleaning up when libuv is unloaded by means of `dlclose(3)`.

Fixes: https://github.com/libuv/libuv/issues/2763
PR-URL: https://github.com/libuv/libuv/pull/2764
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>

docs/src/misc.rst

@@ -233,6 +233,22 @@ API
                  sure the allocator is changed while no memory was allocated with
                  the previous allocator, or that they are compatible.
 
+.. c:function:: void uv_library_shutdown(void);
+
+    .. versionadded:: 1.38.0
+
+    Release any global state that libuv is holding onto. Libuv will normally
+    do so automatically when it is unloaded but it can be instructed to perform
+    cleanup manually.
+
+    .. warning:: Only call :c:func:`uv_library_shutdown()` once.
+
+    .. warning:: Don't call :c:func:`uv_library_shutdown()` when there are
+    still event loops or I/O requests active.
+
+    .. warning:: Don't call libuv functions after calling
+    :c:func:`uv_library_shutdown()`.
+
 .. c:function:: uv_buf_t uv_buf_init(char* base, unsigned int len)
 
     Constructor for :c:type:`uv_buf_t`.

include/uv.h

@@ -265,6 +265,8 @@ typedef void* (*uv_realloc_func)(void* ptr, size_t size);
 typedef void* (*uv_calloc_func)(size_t count, size_t size);
 typedef void (*uv_free_func)(void* ptr);
 
+UV_EXTERN void uv_library_shutdown(void);
+
 UV_EXTERN int uv_replace_allocator(uv_malloc_func malloc_func,
                                    uv_realloc_func realloc_func,
                                    uv_calloc_func calloc_func,

src/threadpool.c

@@ -160,8 +160,8 @@ static void post(QUEUE* q, enum uv__work_kind kind) {
 }
 
 
+void uv__threadpool_cleanup(void) {
 #ifndef _WIN32
-UV_DESTRUCTOR(static void cleanup(void)) {
   unsigned int i;
 
   if (nthreads == 0)
@@ -181,8 +181,8 @@ UV_DESTRUCTOR(static void cleanup(void)) {
 
   threads = NULL;
   nthreads = 0;
-}
 #endif
+}
 
 
 static void init_threads(void) {

src/unix/aix.c

@@ -926,7 +926,7 @@ int uv_get_process_title(char* buffer, size_t size) {
 }
 
 
-UV_DESTRUCTOR(static void free_args_mem(void)) {
+void uv__process_title_cleanup(void) {
   uv__free(args_mem);  /* Keep valgrind happy. */
   args_mem = NULL;
 }

src/unix/bsd-proctitle.c

@@ -37,6 +37,13 @@ static void init_process_title_mutex_once(void) {
 }
 
 
+void uv__process_title_cleanup(void) {
+  /* TODO(bnoordhuis) uv_mutex_destroy(&process_title_mutex)
+   * and reset process_title_mutex_once?
+   */
+}
+
+
 char** uv_setup_args(int argc, char** argv) {
   process_title = argc > 0 ? uv__strdup(argv[0]) : NULL;
   return argv;

src/unix/internal.h

@@ -106,10 +106,8 @@ int uv__pthread_sigmask(int how, const sigset_t* set, sigset_t* oset);
 #if defined(__clang__) ||                                                     \
     defined(__GNUC__) ||                                                      \
     defined(__INTEL_COMPILER)
-# define UV_DESTRUCTOR(declaration) __attribute__((destructor)) declaration
 # define UV_UNUSED(declaration)     __attribute__((unused)) declaration
 #else
-# define UV_DESTRUCTOR(declaration) declaration
 # define UV_UNUSED(declaration)     declaration
 #endif
 

src/unix/no-proctitle.c

@@ -29,6 +29,9 @@ char** uv_setup_args(int argc, char** argv) {
   return argv;
 }
 
+void uv__process_title_cleanup(void) {
+}
+
 int uv_set_process_title(const char* title) {
   return 0;
 }

src/unix/proctitle.c

@@ -145,7 +145,7 @@ int uv_get_process_title(char* buffer, size_t size) {
 }
 
 
-UV_DESTRUCTOR(static void free_args_mem(void)) {
+void uv__process_title_cleanup(void) {
   uv__free(args_mem);  /* Keep valgrind happy. */
   args_mem = NULL;
 }

src/unix/signal.c

@@ -77,7 +77,7 @@ static void uv__signal_global_init(void) {
 }
 
 
-UV_DESTRUCTOR(static void uv__signal_global_fini(void)) {
+void uv__signal_cleanup(void) {
   /* We can only use signal-safe functions here.
    * That includes read/write and close, fortunately.
    * We do all of this directly here instead of resetting
@@ -98,7 +98,7 @@ UV_DESTRUCTOR(static void uv__signal_global_fini(void)) {
 
 
 static void uv__signal_global_reinit(void) {
-  uv__signal_global_fini();
+  uv__signal_cleanup();
 
   if (uv__make_pipe(uv__signal_lock_pipefd, 0))
     abort();

src/uv-common.c

@@ -821,3 +821,19 @@ void uv_free_cpu_info(uv_cpu_info_t* cpu_infos, int count) {
 
   uv__free(cpu_infos);
 }
+
+
+#ifdef __GNUC__  /* Also covers __clang__ and __INTEL_COMPILER. */
+__attribute__((destructor))
+#endif
+void uv_library_shutdown(void) {
+  static int was_shutdown;
+
+  if (was_shutdown)
+    return;
+
+  uv__process_title_cleanup();
+  uv__signal_cleanup();
+  uv__threadpool_cleanup();
+  was_shutdown = 1;
+}

src/uv-common.h

@@ -201,6 +201,10 @@ int uv__next_timeout(const uv_loop_t* loop);
 void uv__run_timers(uv_loop_t* loop);
 void uv__timer_close(uv_timer_t* handle);
 
+void uv__process_title_cleanup(void);
+void uv__signal_cleanup(void);
+void uv__threadpool_cleanup(void);
+
 #define uv__has_active_reqs(loop)                                             \
   ((loop)->active_reqs.count > 0)
 

src/win/signal.c

@@ -46,6 +46,11 @@ void uv_signals_init(void) {
 }
 
 
+void uv__signal_cleanup(void) {
+  /* TODO(bnoordhuis) Undo effects of uv_signal_init()? */
+}
+
+
 static int uv__signal_compare(uv_signal_t* w1, uv_signal_t* w2) {
   /* Compare signums first so all watchers with the same signnum end up
    * adjacent. */

src/win/util.c

@@ -361,6 +361,10 @@ char** uv_setup_args(int argc, char** argv) {
 }
 
 
+void uv__process_title_cleanup(void) {
+}
+
+
 int uv_set_process_title(const char* title) {
   int err;
   int length;

test/task.h

@@ -230,6 +230,7 @@ typedef enum {
   do {                                              \
     close_loop(uv_default_loop());                  \
     ASSERT(0 == uv_loop_close(uv_default_loop()));  \
+    uv_library_shutdown();                          \
   } while (0)
 
 /* Just sugar for wrapping the main() for a task or helper. */