unix: switch to c11 atomics

Fixes: #3683

Author: bnoordhuis

Makefile.am

@@ -96,7 +96,6 @@ else  # WINNT
 uvinclude_HEADERS += include/uv/unix.h
 AM_CPPFLAGS += -I$(top_srcdir)/src/unix
 libuv_la_SOURCES += src/unix/async.c \
-                   src/unix/atomic-ops.h \
                    src/unix/core.c \
                    src/unix/dl.c \
                    src/unix/fs.c \
@@ -110,7 +109,6 @@ libuv_la_SOURCES += src/unix/async.c \
                    src/unix/process.c \
                    src/unix/random-devurandom.c \
                    src/unix/signal.c \
-                   src/unix/spinlock.h \
                    src/unix/stream.c \
                    src/unix/tcp.c \
                    src/unix/thread.c \

src/unix/async.c

@@ -24,9 +24,9 @@
 
 #include "uv.h"
 #include "internal.h"
-#include "atomic-ops.h"
 
 #include <errno.h>
+#include <stdatomic.h>
 #include <stdio.h>  /* snprintf() */
 #include <assert.h>
 #include <stdlib.h>
@@ -40,6 +40,7 @@
 
 static void uv__async_send(uv_loop_t* loop);
 static int uv__async_start(uv_loop_t* loop);
+static void uv__cpu_relax(void);
 
 
 int uv_async_init(uv_loop_t* loop, uv_async_t* handle, uv_async_cb async_cb) {
@@ -61,19 +62,26 @@ int uv_async_init(uv_loop_t* loop, uv_async_t* handle, uv_async_cb async_cb) {
 
 
 int uv_async_send(uv_async_t* handle) {
+  _Atomic int* pending;
+  int expected;
+
+  pending = (_Atomic int*) &handle->pending;
+
   /* Do a cheap read first. */
-  if (ACCESS_ONCE(int, handle->pending) != 0)
+  if (atomic_load_explicit(pending, memory_order_relaxed) != 0)
     return 0;
 
   /* Tell the other thread we're busy with the handle. */
-  if (cmpxchgi(&handle->pending, 0, 1) != 0)
+  expected = 0;
+  if (!atomic_compare_exchange_strong(pending, &expected, 1))
     return 0;
 
   /* Wake up the other thread's event loop. */
   uv__async_send(handle->loop);
 
   /* Tell the other thread we're done. */
-  if (cmpxchgi(&handle->pending, 1, 2) != 1)
+  expected = 1;
+  if (!atomic_compare_exchange_strong(pending, &expected, 2))
     abort();
 
   return 0;
@@ -82,8 +90,11 @@ int uv_async_send(uv_async_t* handle) {
 
 /* Only call this from the event loop thread. */
 static int uv__async_spin(uv_async_t* handle) {
+  _Atomic int* pending;
+  int expected;
   int i;
-  int rc;
+
+  pending = (_Atomic int*) &handle->pending;
 
   for (;;) {
     /* 997 is not completely chosen at random. It's a prime number, acyclical
@@ -94,13 +105,14 @@ static int uv__async_spin(uv_async_t* handle) {
        * rc=1 -- handle is pending, other thread is still working with it.
        * rc=2 -- handle is pending, other thread is done.
        */
-      rc = cmpxchgi(&handle->pending, 2, 0);
+      expected = 2;
+      atomic_compare_exchange_strong(pending, &expected, 0);
 
-      if (rc != 1)
-        return rc;
+      if (expected != 1)
+        return expected;
 
       /* Other thread is busy with this handle, spin until it's done. */
-      cpu_relax();
+      uv__cpu_relax();
     }
 
     /* Yield the CPU. We may have preempted the other thread while it's
@@ -251,3 +263,16 @@ void uv__async_stop(uv_loop_t* loop) {
   uv__close(loop->async_io_watcher.fd);
   loop->async_io_watcher.fd = -1;
 }
+
+
+static void uv__cpu_relax(void) {
+#if defined(__i386__) || defined(__x86_64__)
+  __asm__ __volatile__ ("rep; nop" ::: "memory");  /* a.k.a. PAUSE */
+#elif (defined(__arm__) && __ARM_ARCH >= 7) || defined(__aarch64__)
+  __asm__ __volatile__ ("yield" ::: "memory");
+#elif (defined(__ppc__) || defined(__ppc64__)) && defined(__APPLE__)
+  __asm volatile ("" : : : "memory");
+#elif !defined(__APPLE__) && (defined(__powerpc64__) || defined(__ppc64__) || defined(__PPC64__))
+  __asm__ __volatile__ ("or 1,1,1; or 2,2,2" ::: "memory");
+#endif
+}

src/unix/atomic-ops.h

@@ -21,8 +21,8 @@
 
 #include "uv.h"
 #include "internal.h"
-#include "spinlock.h"
 
+#include <stdatomic.h>
 #include <stdlib.h>
 #include <assert.h>
 #include <unistd.h>
@@ -64,7 +64,7 @@ static int isreallyatty(int file) {
 
 static int orig_termios_fd = -1;
 static struct termios orig_termios;
-static uv_spinlock_t termios_spinlock = UV_SPINLOCK_INITIALIZER;
+static _Atomic int termios_spinlock = 0;
 
 int uv__tcsetattr(int fd, int how, const struct termios *term) {
   int rc;
@@ -280,6 +280,7 @@ static void uv__tty_make_raw(struct termios* tio) {
 
 int uv_tty_set_mode(uv_tty_t* tty, uv_tty_mode_t mode) {
   struct termios tmp;
+  int expected;
   int fd;
   int rc;
 
@@ -296,12 +297,16 @@ int uv_tty_set_mode(uv_tty_t* tty, uv_tty_mode_t mode) {
       return UV__ERR(errno);
 
     /* This is used for uv_tty_reset_mode() */
-    uv_spinlock_lock(&termios_spinlock);
+    do
+      expected = 0;
+    while (!atomic_compare_exchange_strong(&termios_spinlock, &expected, 1));
+
     if (orig_termios_fd == -1) {
       orig_termios = tty->orig_termios;
       orig_termios_fd = fd;
     }
-    uv_spinlock_unlock(&termios_spinlock);
+
+    atomic_store(&termios_spinlock, 0);
   }
 
   tmp = tty->orig_termios;
@@ -442,17 +447,20 @@ uv_handle_type uv_guess_handle(uv_file file) {
  */
 int uv_tty_reset_mode(void) {
   int saved_errno;
+  int expected;
   int err;
 
   saved_errno = errno;
-  if (!uv_spinlock_trylock(&termios_spinlock))
+
+  expected = 0;
+  if (!atomic_compare_exchange_strong(&termios_spinlock, &expected, 1))
     return UV_EBUSY;  /* In uv_tty_set_mode(). */
 
   err = 0;
   if (orig_termios_fd != -1)
     err = uv__tcsetattr(orig_termios_fd, TCSANOW, &orig_termios);
 
-  uv_spinlock_unlock(&termios_spinlock);
+  atomic_store(&termios_spinlock, 0);
   errno = saved_errno;
 
   return err;