Add loop:fork() API, remove dependency on pthread, and stop calling ev_default_fork automatically.

Author: Brian Maher

README

@@ -54,6 +54,12 @@ Choosing a backend:
 
     Please see the documentation for libev for more details.
 
+WARNING:
+
+  If your program fork()s, then you will need to re-initialize
+  your event loop(s) in the child process.  You can do this
+  re-initialization using the loop:fork() function.
+
 -- ev functions --
 
 major, minor = ev.version()
@@ -167,6 +173,11 @@ ev.SIGNAL (constant)
 
 -- ev.Loop object methods --
 
+loop:fork()
+
+   You *must* call this function in the child process after fork(2)
+   system call and before the next iteration of the event loop.
+
 loop:loop()
 
     Run the event loop!  Returns when there are no more watchers

loop_lua_ev.c

@@ -33,6 +33,7 @@ static int create_loop_mt(lua_State *L) {
         { "loop",       loop_loop },
         { "unloop",     loop_unloop },
         { "backend",    loop_backend },
+        { "fork",       loop_fork },
         { "__gc",       loop_delete },
         { NULL, NULL }
     };
@@ -81,9 +82,6 @@ static struct ev_loop** check_loop_and_init(lua_State *L, int loop_i) {
                        " is causing it to select a bad backend?");
         }
         register_obj(L, loop_i, *loop_r);
-
-        /* TODO: Only enable this if linked with pthread: */
-        pthread_atfork(0, 0, ev_default_fork);
     }
     return loop_r;
 }
@@ -262,3 +260,22 @@ static int loop_backend(lua_State *L) {
     lua_pushinteger(L, ev_backend(*check_loop_and_init(L, 1)));
     return 1;
 }
+
+/**
+ * Make it safe to resume an event loop after the fork(2) system call.
+ *
+ * [-0, +0, m]
+ */
+static int loop_fork(lua_State *L) {
+    struct ev_loop* loop = *check_loop(L, 1);
+
+    if ( UNINITIALIZED_DEFAULT_LOOP == loop ) {
+        // Do nothing!
+    } else if ( ev_is_default_loop(loop) ) {
+        ev_default_fork();
+    } else {
+        ev_loop_fork(loop);
+    }
+
+    return 0;
+}

lua-ev.rockspec

@@ -23,16 +23,6 @@ external_dependencies = {
       header = "ev.h",
       library = "libev.so"
    },
-   PTHREADS = {
-      header = "pthread.h",
-   },
-   platforms = {
-      linux = {
-         PTHREADS = {
-           library = "libpthread.so"
-         }
-      }
-   }
 }
 
 build = {
@@ -52,7 +42,7 @@ build = {
          modules = {
             ev = {
                libraries = {
-                  "ev", "pthread"
+                  "ev"
                }
             }
          }

lua_ev.h

@@ -85,6 +85,7 @@ static int               loop_update_now(lua_State *L);
 static int               loop_loop(lua_State *L);
 static int               loop_unloop(lua_State *L);
 static int               loop_backend(lua_State *L);
+static int               loop_fork(lua_State *L);
 
 /**
  * Object functions: