qemurunner.py: fix race condition at qemu startup

When handling pid file, qemu would first create the file, stat it,
lock it and then write actually contents to it.

So it's possbile that when reading the pid file, the content is empty.

[YOCTO #13390]

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

diff --git a/meta/lib/oeqa/utils/qemurunner.py b/meta/lib/oeqa/utils/qemurunner.py
index c16227fc386fe2960d679a75b5a69e593ca3daa4..68684aeb8ab3f9250ea883bfd874f3f85ddbfd5b 100644 (file)
--- a/meta/lib/oeqa/utils/qemurunner.py
+++ b/meta/lib/oeqa/utils/qemurunner.py
@@ -425,13 +425,20 @@ class QemuRunner:
         if not self.runqemu or self.runqemu.poll() is not None:
             return False
         if os.path.isfile(self.qemu_pidfile):
-            f = open(self.qemu_pidfile, 'r')
-            qemu_pid = f.read()
-            f.close()
-            qemupid = int(qemu_pid)
-            if os.path.exists("/proc/" + str(qemupid)):
-                self.qemupid = qemupid
-                return True
+            # when handling pidfile, qemu creates the file, stat it, lock it and then write to it
+            # so it's possible that the file has been created but the content is empty
+            pidfile_timeout = time.time() + 3
+            while time.time() < pidfile_timeout:
+                with open(self.qemu_pidfile, 'r') as f:
+                    qemu_pid = f.read().strip()
+                # file created but not yet written contents
+                if not qemu_pid:
+                    time.sleep(0.5)
+                    continue
+                else:
+                    if os.path.exists("/proc/" + qemu_pid):
+                        self.qemupid = int(qemu_pid)
+                        return True
         return False
 
     def run_serial(self, command, raw=False, timeout=60):