bitbake: server/process: Ensure we don't keep looping if some other server is started

Showing "leftover process" messages when a new server has started and is being
used by some UI is horrible. Compare the PID data from the lockfile to
avoid this (and the ton of confusing log data it generates).

Also, move the time.sleep() call to be after the first lock attempt, which
reduces noise in the logs significantly.

(Bitbake rev: ce1897a31afb5a14997bc3d2f459b90d43eecb7d)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/server/process.py

@@ -266,6 +266,17 @@ class ProcessServer():
         # Finally release the lockfile but warn about other processes holding it open
         lock = self.bitbake_lock
         lockfile = self.bitbake_lock_name
+
+        def get_lock_contents(lockfile):
+            try:
+                with open(lockfile, "r") as f:
+                    return f.readlines()
+            except FileNotFoundError:
+                return None
+
+        lockcontents = get_lock_contents(lockfile)
+        serverlog("Original lockfile contents: " + str(lockcontents))
+
         lock.close()
         lock = None
 
@@ -273,14 +284,22 @@ class ProcessServer():
             i = 0
             lock = None
             while not lock and i < 30:
-                time.sleep(0.1)
                 lock = bb.utils.lockfile(lockfile, shared=False, retry=False, block=False)
+                if not lock:
+                    newlockcontents = get_lock_contents(lockfile)
+                    if newlockcontents != lockcontents:
+                        # A new server was started, the lockfile contents changed, we can exit
+                        serverlog("Lockfile now contains different contents, exiting: " + str(newlockcontents))
+                        return
+                    time.sleep(0.1)
                 i += 1
             if lock:
                 # We hold the lock so we can remove the file (hide stale pid data)
                 # via unlockfile.
                 bb.utils.unlockfile(lock)
+                serverlog("Exiting as we could obtain the lock")
                 return
+
             if not lock:
                 # Some systems may not have lsof available
                 procs = None