Eve document count broken with concurrent requests #1271
Description
This issue affects Eve when it is executed either on the Flask's development server with the default multi-threaded configuration, or when deployed in a production server such as Gunicorn using an async worker type (e.g. gevent).
Expected Behavior
For a given GET request, Eve should always return the proper document count in the _meta field, based on the client requested filter.
Actual Behavior
When performing multiple concurrent GET requests, in the scenario described above, there is a high chance of getting wrong results for the document count.
For instance, consider the following resource:
{
"_id": 1,
"value": "a"
},
{
"_id": 2,
"value": "a"
},
{
"_id": 3,
"value": "b"
}If we perform the following two concurrent requests:
1. GET http://server/resource?where={"value": "a"}
2. GET http://server/resource?where={"value": "b"}
There is a high change of getting the following wrong results:
1.
{
"_items": [
{
"_id": 1,
"value": "a"
},
{
"_id": 2,
"value": "a"
}
],
"_meta": {
"total": 2
}
}
2.
{
"_items": [
{
"_id": 3,
"value": "b"
}
],
"_meta": {
"total": 2 <---------------- WRONG!!!!
}
}
or:
1.
{
"_items": [
{
"_id": 1,
"value": "a"
},
{
"_id": 2,
"value": "a"
}
],
"_meta": {
"total": 1 <---------------- WRONG!!!!
}
}
2.
{
"_items": [
{
"_id": 3,
"value": "b"
}
],
"_meta": {
"total": 1
}
}
This seems to be caused by the changes introduced in 61de6d8 and ac3bd78. With these changes, Eve stores the last used cursor and filter specification in a global object and later uses them to retrieve the document count. This can lead to the above issues when document count is accessed in a concurrent/async way for multiple requests/
Environment
- Python version: 3.7.0
- Eve version: 0.9
- Flask version: 1.0.2
- Gunicorn version: 19.9.0
- Gevent version: 1.4.0