perf: on Linux, use malloc_trim to release memory.

ref:
http://www.cplusplus-soup.com/2010/01/freedelete-not-returning-memory-to-os.html
https://lemire.me/blog/2020/03/03/calling-free-or-delete/

src/blrec/core/stream_recorder.py

@@ -8,6 +8,7 @@ from blrec.bili.typing import QualityNumber, StreamFormat
 from blrec.event.event_emitter import EventEmitter
 from blrec.flv.operators import MetaData, StreamProfile
 from blrec.setting.typing import RecordingMode
+from blrec.utils.libc import malloc_trim
 from blrec.utils.mixins import AsyncStoppableMixin
 
 from .flv_stream_recorder_impl import FLVStreamRecorderImpl
@@ -255,6 +256,7 @@ class StreamRecorder(
 
     async def _do_stop(self) -> None:
         await self._impl.stop()
+        malloc_trim(0)
 
     async def on_video_file_created(self, path: str, record_start_time: int) -> None:
         await self._emit('video_file_created', path, record_start_time)

src/blrec/task/task_manager.py

@@ -7,6 +7,8 @@ from typing import TYPE_CHECKING, Dict, Iterator, Optional
 import aiohttp
 from tenacity import retry, retry_if_exception_type, stop_after_delay, wait_exponential
 
+from blrec.utils.libc import malloc_trim
+
 from ..bili.exceptions import ApiRequestError
 from ..exception import NotFoundError, submit_exception
 from ..flv.operators import MetaData, StreamProfile
@@ -17,8 +19,8 @@ if TYPE_CHECKING:
     from ..setting import SettingsManager
 
 from ..setting import (
-    DanmakuSettings,
     BiliApiSettings,
+    DanmakuSettings,
     HeaderSettings,
     OutputSettings,
     PostprocessingSettings,
@@ -57,6 +59,7 @@ class RecordTaskManager:
             return
         await asyncio.wait([t.destroy() for t in self._tasks.values() if t.ready])
         self._tasks.clear()
+        malloc_trim(0)
         logger.info('Successfully destroyed all task')
 
     def has_task(self, room_id: int) -> bool:
@@ -115,11 +118,13 @@ class RecordTaskManager:
         await task.disable_monitor()
         await task.destroy()
         del self._tasks[room_id]
+        malloc_trim(0)
 
     async def remove_all_tasks(self) -> None:
         coros = [self.remove_task(i) for i, t in self._tasks.items() if t.ready]
         if coros:
             await asyncio.wait(coros)
+        malloc_trim(0)
 
     async def start_task(self, room_id: int) -> None:
         task = self._get_task(room_id, check_ready=True)

src/blrec/utils/libc.py

@@ -0,0 +1,16 @@
+from ctypes import cdll
+from ctypes.util import find_library
+
+lib_name = find_library('c')
+if not lib_name:
+    libc = None
+else:
+    libc = cdll.LoadLibrary(lib_name)
+
+
+def malloc_trim(pad: int) -> bool:
+    """Release free memory from the heap"""
+    assert pad >= 0, 'pad must be >= 0'
+    if libc is None:
+        return False
+    return libc.malloc_trim(pad) == 1