[batch] job FIFO scheduler as baseline (#231)

* job FIFO scheduler as baseline

* update comments

* func name and typo

---------

Co-authored-by: xin.chen <[email protected]>

Author: xinchen384

python/aibrix/aibrix/batch/scheduler.py

@@ -0,0 +1,120 @@
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# 	http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from enum import Enum
+import time
+import asyncio
+import bisect
+import queue
+
+# This is the time interval for the sliding window to check.
+EXPIRE_INTERVAL = 1
+
+
+class SchedulePolicy(Enum):
+    FIFO = 1
+
+
+class JobScheduler:
+    def __init__(self, policy=SchedulePolicy.FIFO):
+        """
+        self._jobs_queue are all the jobs.
+        self._due_jobs_list stores all potential jobs that can be marked
+        as expired jobs.
+        self._inactive_jobs are jobs that are already invalid.
+        """
+        self.interval = EXPIRE_INTERVAL
+        self._jobs_queue = queue.Queue()
+        self._inactive_jobs = set()
+        self._due_jobs_list = []
+        # Start sliding process in an async way
+        asyncio.create_task(self.job_cleanup_loop())
+        self._policy = policy
+
+    def append_job(self, job_id, due_time_seconds):
+        # This submits a job to scheduler. The scheduler will determine
+        # which job gets executed.
+        self._jobs_queue.put(job_id)
+
+        def key_func(x):
+            return x[1]
+
+        current_time = time.time()
+        due_time = current_time + due_time_seconds
+        item = (job_id, due_time)
+        index = bisect.bisect_left(
+            [key_func(t) for t in self._due_jobs_list], key_func(item)
+        )
+        self._due_jobs_list.insert(index, item)
+
+    def schedule_get_job(self):
+        # Scheduler outputs a job to be processed following the specified policy.
+        job_id = None
+
+        # [TODO] use class abstraction for SchedulingPolicy
+        if self._policy == SchedulePolicy.FIFO:
+            if not self._jobs_queue.empty():
+                job_id = self._jobs_queue.get()
+
+            # Every time when popping a job from queue,
+            # we check if this job is in active state.
+            while (
+                job_id
+                and job_id in self._inactive_jobs
+                and not self._jobs_queue.empty()
+            ):
+                job_id = self._jobs_queue.get()
+
+        else:
+            print("Unsupported scheduling policy!")
+
+        return job_id
+
+    def get_inactive_jobs(self):
+        return self._inactive_jobs
+
+    async def expire_jobs(self):
+        # This is to expire jobs based on specified due time per job.
+        if self._policy == SchedulePolicy.FIFO:
+            current_time = time.time()
+            idx = 0
+            while (
+                idx < len(self._due_jobs_list)
+                and self._due_jobs_list[idx][1] <= current_time
+            ):
+                idx += 1
+
+            print("Number of expired jobs is ", idx)
+            for i in range(idx):
+                # Update job's status to job manager
+                job_id = self._due_jobs_list[i][0]
+                self._inactive_jobs.add(job_id)
+                print("======> ", job_id, "expired.")
+            self._due_jobs_list = self._due_jobs_list[idx:]
+        else:
+            print("Unsupported scheduling policy!")
+
+    async def job_cleanup_loop(self):
+        """
+        This is a long-running process to check if jobs have expired or not.
+        """
+        round_id = 0
+        while True:
+            start_time = time.time()  # Record start time
+            await self.expire_jobs()  # Run the process
+            elapsed_time = time.time() - start_time  # Calculate elapsed time
+            time_to_next_run = max(
+                0, self.interval - elapsed_time
+            )  # Calculate remaining time
+            print("Sliding, round: ", round_id)
+            round_id += 1
+            await asyncio.sleep(time_to_next_run)  # Wait for the remaining time