Also add semaphore for exports

api/config.dev.py

@@ -30,5 +30,6 @@ ADDITIONAL_CORS_ORIGINS = [
     "http://localhost:8888/",  # for maputnik on 8888
 ]
 TILE_SEMAPHORE_SIZE = 4
+EXPORT_SEMAPHORE_SIZE = 4
 
 # vim: set ft=python :

api/config.py.example

@@ -66,4 +66,8 @@ ADDITIONAL_CORS_ORIGINS = None
 # to the other features of the API ;)
 TILE_SEMAPHORE_SIZE = 4
 
+# How many asynchronous requests may generate exported data simultaneously.
+# Keep this small.
+EXPORT_SEMAPHORE_SIZE = 1
+
 # vim: set ft=python :

api/obs/api/app.py

@@ -70,6 +70,7 @@ app.config.update(
         FRONTEND_HTTPS=True,
         TILES_FILE=None,
         TILE_SEMAPHORE_SIZE=4,
+        EXPORT_SEMAPHORE_SIZE=1,
     )
 )
 
@@ -187,7 +188,10 @@ async def app_connect_db(app, loop):
     app.ctx._db_engine = await app.ctx._db_engine_ctx.__aenter__()
 
     if app.config.TILE_SEMAPHORE_SIZE:
-        app.ctx._tile_semaphore = asyncio.Semaphore(app.config.TILE_SEMAPHORE_SIZE)
+        app.ctx.tile_semaphore = asyncio.Semaphore(app.config.TILE_SEMAPHORE_SIZE)
+
+    if app.config.EXPORT_SEMAPHORE_SIZE:
+        app.ctx.export_semaphore = asyncio.Semaphore(app.config.EXPORT_SEMAPHORE_SIZE)
 
 
 @app.after_server_stop

api/obs/api/routes/exports.py

@@ -12,6 +12,7 @@ from sanic.response import raw
 from sanic.exceptions import InvalidUsage
 
 from obs.api.app import api, json as json_response
+from obs.api.utils import use_request_semaphore
 
 
 class ExportFormat(str, Enum):
@@ -60,60 +61,61 @@ def shapefile_zip():
 
 @api.get(r"/export/events")
 async def export_events(req):
-    bbox = req.ctx.get_single_arg(
-        "bbox", default="-180,-90,180,90", convert=parse_bounding_box
-    )
-    fmt = req.ctx.get_single_arg("fmt", convert=ExportFormat)
-
-    events = await req.ctx.db.stream_scalars(
-        select(OvertakingEvent).where(
-            OvertakingEvent.geometry.bool_op("&&")(func.ST_Transform(bbox, 3857))
+    async with use_request_semaphore(req, "export_semaphore", timeout=30):
+        bbox = req.ctx.get_single_arg(
+            "bbox", default="-180,-90,180,90", convert=parse_bounding_box
         )
-    )
+        fmt = req.ctx.get_single_arg("fmt", convert=ExportFormat)
 
-    if fmt == ExportFormat.SHAPEFILE:
-        with shapefile_zip() as (writer, zip_buffer):
-            writer.field("distance_overtaker", "N", decimal=4)
-            writer.field("distance_stationary", "N", decimal=4)
-            writer.field("way_id", "N", decimal=0)
-            writer.field("direction", "N", decimal=0)
-            writer.field("course", "N", decimal=4)
-            writer.field("speed", "N", decimal=4)
+        events = await req.ctx.db.stream_scalars(
+            select(OvertakingEvent).where(
+                OvertakingEvent.geometry.bool_op("&&")(func.ST_Transform(bbox, 3857))
+            )
+        )
 
+        if fmt == ExportFormat.SHAPEFILE:
+            with shapefile_zip() as (writer, zip_buffer):
+                writer.field("distance_overtaker", "N", decimal=4)
+                writer.field("distance_stationary", "N", decimal=4)
+                writer.field("way_id", "N", decimal=0)
+                writer.field("direction", "N", decimal=0)
+                writer.field("course", "N", decimal=4)
+                writer.field("speed", "N", decimal=4)
+
+                async for event in events:
+                    writer.point(event.longitude, event.latitude)
+                    writer.record(
+                        distance_overtaker=event.distance_overtaker,
+                        distance_stationary=event.distance_stationary,
+                        direction=-1 if event.direction_reversed else 1,
+                        way_id=event.way_id,
+                        course=event.course,
+                        speed=event.speed,
+                        # "time"=event.time,
+                    )
+
+            return raw(zip_buffer.getbuffer())
+
+        if fmt == ExportFormat.GEOJSON:
+            features = []
             async for event in events:
-                writer.point(event.longitude, event.latitude)
-                writer.record(
-                    distance_overtaker=event.distance_overtaker,
-                    distance_stationary=event.distance_stationary,
-                    direction=-1 if event.direction_reversed else 1,
-                    way_id=event.way_id,
-                    course=event.course,
-                    speed=event.speed,
-                    # "time"=event.time,
+                features.append(
+                    {
+                        "type": "Feature",
+                        "geometry": json.loads(event.geometry),
+                        "properties": {
+                            "distance_overtaker": event.distance_overtaker,
+                            "distance_stationary": event.distance_stationary,
+                            "direction": -1 if event.direction_reversed else 1,
+                            "way_id": event.way_id,
+                            "course": event.course,
+                            "speed": event.speed,
+                            "time": event.time,
+                        },
+                    }
                 )
 
-        return raw(zip_buffer.getbuffer())
+            geojson = {"type": "FeatureCollection", "features": features}
+            return json_response(geojson)
 
-    if fmt == ExportFormat.GEOJSON:
-        features = []
-        async for event in events:
-            features.append(
-                {
-                    "type": "Feature",
-                    "geometry": json.loads(event.geometry),
-                    "properties": {
-                        "distance_overtaker": event.distance_overtaker,
-                        "distance_stationary": event.distance_stationary,
-                        "direction": -1 if event.direction_reversed else 1,
-                        "way_id": event.way_id,
-                        "course": event.course,
-                        "speed": event.speed,
-                        "time": event.time,
-                    },
-                }
-            )
-
-        geojson = {"type": "FeatureCollection", "features": features}
-        return json_response(geojson)
-
-    raise InvalidUsage("unknown export format")
+        raise InvalidUsage("unknown export format")

api/obs/api/routes/tiles.py

@@ -1,18 +1,16 @@
-import asyncio
-from contextlib import asynccontextmanager
 from gzip import decompress
 from sqlite3 import connect
 from datetime import datetime, time, timedelta
 from typing import Optional, Tuple
 
 import dateutil.parser
-from sanic.exceptions import Forbidden, InvalidUsage, ServiceUnavailable
+from sanic.exceptions import Forbidden, InvalidUsage
 from sanic.response import raw
 
-from sqlalchemy import select, text
-from sqlalchemy.sql.expression import table, column
+from sqlalchemy import text
 
 from obs.api.app import app
+from obs.api.utils import use_request_semaphore
 
 
 def get_tile(filename, zoom, x, y):
@@ -87,41 +85,9 @@ def get_filter_options(
     return user_id, start, end
 
 
-@asynccontextmanager
-async def use_tile_semaphore(req, timeout=10):
-    """
-    If configured, acquire a semaphore for the map tile request and release it
-    after the context has finished.
-
-    If the semaphore cannot be acquired within the timeout, issue a 503 Service
-    Unavailable error response that describes that the map tile database is
-    overloaded, so users know what the problem is.
-
-    Operates as a noop when the tile semaphore is not enabled.
-    """
-    sem = getattr(req.app.ctx, "_tile_semaphore", None)
-
-    if sem is None:
-        yield
-        return
-
-    try:
-        await asyncio.wait_for(sem.acquire(), timeout)
-
-        try:
-            yield
-        finally:
-            sem.release()
-
-    except asyncio.TimeoutError:
-        raise ServiceUnavailable(
-            "Too many map content requests, database overloaded. Please retry later."
-        )
-
-
 @app.route(r"/tiles/<zoom:int>/<x:int>/<y:(\d+)\.pbf>")
 async def tiles(req, zoom: int, x: int, y: str):
-    async with use_tile_semaphore(req):
+    async with use_request_semaphore(req, "tile_semaphore"):
         if app.config.get("TILES_FILE"):
             tile = get_tile(req.app.config.TILES_FILE, int(zoom), int(x), int(y))
 

api/obs/api/utils.py

@@ -1,12 +1,13 @@
+import asyncio
+from contextlib import asynccontextmanager
 from datetime import datetime
 import logging
+from os.path import commonpath, join, relpath
 import queue
 import tarfile
-from os.path import commonpath, relpath, join
 
 import dateutil.parser
-
-from sanic.exceptions import InvalidUsage
+from sanic.exceptions import InvalidUsage, ServiceUnavailable
 
 log = logging.getLogger(__name__)
 
@@ -127,3 +128,35 @@ class StreamerHelper:
                 await self.response.send(tosend)
             except queue.Empty:
                 break
+
+
+@asynccontextmanager
+async def use_request_semaphore(req, semaphore_name, timeout=10):
+    """
+    If configured, acquire a semaphore for the map tile request and release it
+    after the context has finished.
+
+    If the semaphore cannot be acquired within the timeout, issue a 503 Service
+    Unavailable error response that describes that the database is overloaded,
+    so users know what the problem is.
+
+    Operates as a noop when the tile semaphore is not enabled.
+    """
+    semaphore = getattr(req.app.ctx, semaphore_name, None)
+
+    if semaphore is None:
+        yield
+        return
+
+    try:
+        await asyncio.wait_for(semaphore.acquire(), timeout)
+
+        try:
+            yield
+        finally:
+            semaphore.release()
+
+    except asyncio.TimeoutError:
+        raise ServiceUnavailable(
+            "Too many requests, database overloaded. Please retry later."
+        )