Improved `check_online()` robustness (#10000)

* Improved check_online() robustness 

YOLOv5-wide improvement, not just in check_requirements()

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>

* Update general.py

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>

utils/general.py

@@ -283,11 +283,16 @@ def file_size(path):
 def check_online():
     # Check internet connectivity
     import socket
-    try:
-        socket.create_connection(("1.1.1.1", 443), 5)  # check host accessibility
-        return True
-    except OSError:
-        return False
+
+    def run_once():
+        # Check once
+        try:
+            socket.create_connection(("1.1.1.1", 443), 5)  # check host accessibility
+            return True
+        except OSError:
+            return False
+
+    return run_once() or run_once()  # check twice to increase robustness to intermittent connectivity issues
 
 
 def git_describe(path=ROOT):  # path must be a directory
@@ -369,7 +374,7 @@ def check_requirements(requirements=ROOT / 'requirements.txt', exclude=(), insta
     if s and install and AUTOINSTALL:  # check environment variable
         LOGGER.info(f"{prefix} YOLOv5 requirement{'s' * (n > 1)} {s}not found, attempting AutoUpdate...")
         try:
-            assert check_online() or check_online(), "AutoUpdate skipped (offline)"
+            assert check_online(), "AutoUpdate skipped (offline)"
             LOGGER.info(check_output(f'pip install {s} {cmds}', shell=True).decode())
             source = file if 'file' in locals() else requirements
             s = f"{prefix} {n} package{'s' * (n > 1)} updated per {source}\n" \