Use higher-level wrappers for the __forkHandler global

uvloop/handles/process.pyx

@@ -77,7 +77,7 @@ cdef class UVProcess(UVHandle):
             loop.active_process_handler = self
             __forking = 1
             __forking_loop = loop
-            __forkHandler = <OnForkHandler>&__get_fork_handler
+            system.setForkHandler(<system.OnForkHandler>&__get_fork_handler)
 
             PyOS_BeforeFork()
 
@@ -87,7 +87,7 @@ cdef class UVProcess(UVHandle):
 
             __forking = 0
             __forking_loop = None
-            __forkHandler = NULL
+            system.resetForkHandler()
             loop.active_process_handler = None
 
             PyOS_AfterFork_Parent()

uvloop/includes/fork_handler.h

@@ -8,8 +8,20 @@ OnForkHandler __forkHandler = NULL;
 Note: Fork handler needs to be in C (not cython) otherwise it would require
 GIL to be present, but some forks can exec non-python processes.
 */
-void handleAtFork() {
+void handleAtFork(void) {
     if (__forkHandler != NULL) {
         __forkHandler();
     }
 }
+
+
+void setForkHandler(OnForkHandler handler)
+{
+    __forkHandler = handler;
+}
+
+
+void resetForkHandler(void)
+{
+    __forkHandler = NULL;
+}

uvloop/includes/system.pxd

@@ -81,3 +81,11 @@ cdef extern from "includes/compat.h" nogil:
     int EPOLL_CTL_DEL
     int epoll_ctl(int epfd, int op, int fd, epoll_event *event)
     object MakeUnixSockPyAddr(sockaddr_un *addr)
+
+
+cdef extern from "includes/fork_handler.h":
+
+    ctypedef void (*OnForkHandler)()
+    void handleAtFork()
+    void setForkHandler(OnForkHandler handler)
+    void resetForkHandler()

uvloop/loop.pyx

@@ -3178,11 +3178,6 @@ cdef vint __atfork_installed = 0
 cdef vint __forking = 0
 cdef Loop __forking_loop = None
 
-cdef extern from "includes/fork_handler.h":
-
-    ctypedef void (*OnForkHandler)()
-    cdef OnForkHandler __forkHandler
-    void handleAtFork()
 
 cdef void __get_fork_handler() nogil:
     global __forking
@@ -3201,7 +3196,7 @@ cdef __install_atfork():
 
     cdef int err
 
-    err = system.pthread_atfork(NULL, NULL, &handleAtFork)
+    err = system.pthread_atfork(NULL, NULL, &system.handleAtFork)
     if err:
         __atfork_installed = 0
         raise convert_error(-err)