attempt to work around race condition when you close an fd but there are

still outstanding events queued on it.

io/io_canread.c

@@ -33,6 +33,15 @@ int64 io_canread() {
     e->next_read=-1;
     debug_printf(("io_canread: dequeue %lld from normal read queue (next is %ld)\n",r,first_readable));
 
+    if (e->closed) {
+      /* The fd was previously closed, but there were still open events on it.
+       * To prevent race conditions, we did not actually close the fd
+       * but only marked it as closed, so we can skip this event here
+       * and really closed it now. */
+      io_close(r);
+      continue;
+    }
+
 #ifdef __MINGW32__
 //    printf("event on %d: wr %d rq %d aq %d\n",(int)r,e->wantread,e->readqueued,e->acceptqueued);
 #endif

io/io_canwrite.c

@@ -27,6 +27,16 @@ int64 io_canwrite() {
     r=first_writeable;
     first_writeable=e->next_write;
     e->next_write=-1;
+
+    if (e->closed) {
+      /* The fd was previously closed, but there were still open events on it.
+       * To prevent race conditions, we did not actually close the fd
+       * but only marked it as closed, so we can skip this event here
+       * and really closed it now. */
+      io_close(r);
+      continue;
+    }
+
     debug_printf(("io_canwrite: dequeue %lld from normal write queue (next is %ld)\n",r,first_writeable));
     if (e->wantwrite &&
 #ifdef __MINGW32__

io/io_close.c

@@ -15,8 +15,8 @@ void io_close(int64 d) {
   if ((e=iarray_get(&io_fds,d))) {
     e->inuse=0;
     e->cookie=0;
-    if (e->kernelwantread) io_dontwantread_really(d,e);
-    if (e->kernelwantwrite) io_dontwantwrite_really(d,e);
+    if (e->kernelwantread) { io_dontwantread_really(d,e); e->kernelwantread=0; }
+    if (e->kernelwantwrite) { io_dontwantwrite_really(d,e); e->kernelwantwrite=0; }
     if (e->mmapped) {
 #ifdef __MINGW32__
       UnmapViewOfFile(e->mmapped);
@@ -26,6 +26,17 @@ void io_close(int64 d) {
 #endif
       e->mmapped=0;
     }
+    if (e->next_read!=-1 || e->next_write!=-1) {
+      /* There are still outstanding events. If we close the fd, between
+       * now and when those events are handled, another accept() or
+       * open() could return this descriptor, and cause bad things to
+       * happen for everybody.
+       * So we don't actually close the fd now, but we will mark it as
+       * closed. */
+      e->closed=1;
+      return;
+    } else
+      e->closed=0;
   }
   close(d);
 }

io_internal.h

@@ -46,6 +46,7 @@ typedef struct {
   unsigned int kernelwantread:1;	/* did we tell the kernel we want to read/write? */
   unsigned int kernelwantwrite:1;
   unsigned int epolladded:1;
+  unsigned int closed:1;	/* io_close called, but close deferred because of outstanding events */
 #ifdef __MINGW32__
   unsigned int readqueued:2;
   unsigned int writequeued:2;
@@ -80,6 +81,8 @@ my_extern array io_pollfds;
 my_extern long first_readable;
 my_extern long first_writeable;
 
+my_extern long first_deferred;
+
 my_extern enum __io_waitmode {
   UNDECIDED,
   POLL