Added async support

Incorporated changes from SijmenHuizenga's pull request (dbader#438) to add async support.

schedule/__init__.py

@@ -37,6 +37,8 @@
 [2] https://github.com/Rykian/clockwork
 [3] https://adam.herokuapp.com/past/2010/6/30/replace_cron_with_clockwork/
 """
+import asyncio
+import inspect
 from collections.abc import Hashable
 import datetime
 import functools
@@ -87,7 +89,7 @@ def __init__(self) -> None:
 
     def run_pending(self) -> None:
         """
-        Run all jobs that are scheduled to run.
+        Run all sync jobs that are scheduled to run.
 
         Please note that it is *intended behavior that run_pending()
         does not run missed jobs*. For example, if you've registered a job
@@ -99,9 +101,22 @@ def run_pending(self) -> None:
         for job in sorted(runnable_jobs):
             self._run_job(job)
 
+    async def run_pending_async(self):
+        """
+        Run all sync and async jobs that are scheduled to run.
+
+        Please note that it is *intended behavior that run_pending_async()
+        does not run missed jobs*. For example, if you've registered a job
+        that should run every minute and you only call run_pending()
+        in one hour increments then your job won't be run 60 times in
+        between but only once.
+        """
+        runnable_jobs = (job for job in self.jobs if job.should_run)
+        await asyncio.gather(*[self._run_job_async(job) for job in runnable_jobs])
+
     def run_all(self, delay_seconds: int = 0) -> None:
         """
-        Run all jobs regardless if they are scheduled to run or not.
+        Run all sync jobs regardless if they are scheduled to run or not.
 
         A delay of `delay` seconds is added between each job. This helps
         distribute system load generated by the jobs more evenly
@@ -118,6 +133,25 @@ def run_all(self, delay_seconds: int = 0) -> None:
             self._run_job(job)
             time.sleep(delay_seconds)
 
+    async def run_all_async(self, delay_seconds=0):
+        """
+        Run all sync and async jobs regardless if they are scheduled to run or not.
+
+        A delay of `delay` seconds is added between each job. This helps
+        distribute system load generated by the jobs more evenly
+        over time.
+
+        :param delay_seconds: A delay added between every executed job
+        """
+        logger.debug(
+            "Running *all* %i jobs with %is delay in between",
+            len(self.jobs),
+            delay_seconds,
+        )
+        for job in self.jobs[:]:
+            await self._run_job_async(job)
+            await asyncio.sleep(delay_seconds)
+
     def get_jobs(self, tag: Optional[Hashable] = None) -> List["Job"]:
         """
         Gets scheduled jobs marked with the given tag, or all jobs
@@ -173,6 +207,17 @@ def _run_job(self, job: "Job") -> None:
         if isinstance(ret, CancelJob) or ret is CancelJob:
             self.cancel_job(job)
 
+    async def _run_job_async(self, job: "Job") -> None:
+        ret = job.run()
+        if inspect.isawaitable(ret):
+            ret = await ret
+
+        self._process_job_return_value(job, ret)
+
+    def _process_job_return_value(self, job: "Job", ret: any):
+        if isinstance(ret, CancelJob) or ret is CancelJob:
+            self.cancel_job(job)
+
     def get_next_run(
         self, tag: Optional[Hashable] = None
     ) -> Optional[datetime.datetime]:
@@ -855,6 +900,13 @@ def run_pending() -> None:
     default_scheduler.run_pending()
 
 
+async def run_pending_async() -> None:
+    """Calls :meth:`run_pending_async <Scheduler.run_pending_async>` on the
+    :data:`default scheduler instance <default_scheduler>`.
+    """
+    await default_scheduler.run_pending_async()
+
+
 def run_all(delay_seconds: int = 0) -> None:
     """Calls :meth:`run_all <Scheduler.run_all>` on the
     :data:`default scheduler instance <default_scheduler>`.