Change to wait for all outstanding iothreads before calling fork(). This should prevent a whole host of threading/fork interactions, but may also compromise performance...we'll see.

exec.cpp

@@ -34,6 +34,7 @@
 
 #include "fallback.h"
 #include "util.h"
+#include "iothread.h"
 
 #include "common.h"
 #include "wutil.h"
@@ -833,6 +834,9 @@ static pid_t exec_fork()
 {
     ASSERT_IS_MAIN_THREAD();
     
+    /* Make sure we have no outstanding threads before we fork. This is a pretty sketchy thing to do here, both because exec.cpp shouldn't have to know about iothreads, and because the completion handlers may do unexpected things. */
+    iothread_drain_all();
+    
 	pid_t pid;
 	struct timespec pollint;
 	int i;