Use canStartBuild rather than nextBuild for starting

There is some evidence that a delay in nextBuild can leak to unrelated
workers.
Switch to canStartBuild, whose docs show an example to put the worker
in “quarantine” and avoid the quarantine's exponential backoff
mechanism.

Author: encukou

master/master.cfg

@@ -223,21 +223,22 @@ def get_delay(now, end):
 def no_builds_between(start, end):
     start = datetime.strptime(start, "%H:%M").time()
     end = datetime.strptime(end, "%H:%M").time()
-    def f(builder, requests):
+    @defer.inlineCallbacks
+    def canStartBuild(builder, wfb, request):
         now = datetime.now().time()
         if is_within_time_range(now, start, end):
             delay = get_delay(now, end)
-            # Schedule the build later
-            deferred = defer.Deferred()
-            builder.master.reactor.callLater(
-                int(delay),
-                deferred.callback,
-                requests[0],
-            )
-            return deferred
+            # Adapted from: https://docs.buildbot.net/current/manual/customization.html#canstartbuild-functions
+            wfb.worker.quarantine_timeout = delay
+            wfb.worker.putInQuarantine()
+            # This does not take the worker out of quarantine, it only resets
+            # the timeout value to default (restarting the default
+            # exponential backoff)
+            wfb.worker.resetQuarantine()
+            return False
         # Schedule the build now
-        return requests[0]
-    return f
+        return True
+    return canStartBuild
 
 
 github_status_builders = []
@@ -323,7 +324,7 @@ for branch_num, (git_url, branchname, git_branch) in enumerate(git_branches):
         # This worker runs pyperformance at 12am. If a build is scheduled between
         # 10pm and 2am, it will be delayed at 2am.
         if worker_name == "diegorusso-aarch64-bigmem":
-            builder.nextBuild = no_builds_between("22:00", "2:00")
+            builder.canStartBuild = no_builds_between("22:00", "2:00")
 
         c["builders"].append(builder)
 
@@ -392,7 +393,7 @@ for name, worker_name, buildfactory, stability, tier in BUILDERS:
     # This worker runs pyperformance at 12am. If a build is scheduled between
     # 10pm and 2am, it will be delayed at 2am.
     if worker_name == "diegorusso-aarch64-bigmem":
-        builder.nextBuild = no_builds_between("22:00", "2:00")
+        builder.canStartBuild = no_builds_between("22:00", "2:00")
 
     c["builders"].append(builder)