context.py

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# the Apache License, Version 2.0 (the "License"); you may
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#
# 	http://www.apache.org/licenses/LICENSE-2.0
#
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import contextvars
import time


class RequestContextManager:
    """
    Ensures that request context span the defined scope and allow nesting of request contexts with proper propagation.
    This means that we can span a top-level request context, open sub-request contexts that can be used to measure
    individual timings and still measure the proper total time on the top-level request context.
    """

    def __init__(self, request_context_holder):
        self.ctx_holder = request_context_holder
        self.ctx = None
        self.token = None

    async def __aenter__(self):
        self.ctx, self.token = self.ctx_holder.init_request_context()
        return self

    @property
    def request_start(self):
        return self.ctx["request_start"]

    @property
    def request_end(self):
        return self.ctx["request_end"]

    async def __aexit__(self, exc_type, exc_val, exc_tb):
        # propagate earliest request start and most recent request end to parent
        request_start = self.request_start
        request_end = self.request_end
        self.ctx_holder.restore_context(self.token)
        # don't attempt to restore these values on the top-level context as they don't exist
        if self.token.old_value != contextvars.Token.MISSING:
            self.ctx_holder.update_request_start(request_start)
            self.ctx_holder.update_request_end(request_end)
        self.token = None
        return False


class RequestContextHolder:
    """
    Holds request context variables. This class is only meant to be used together with RequestContextManager.
    """

    request_context = contextvars.ContextVar("rally_request_context")

    def new_request_context(self):
        return RequestContextManager(self)

    @classmethod
    def init_request_context(cls):
        ctx = {}
        token = cls.request_context.set(ctx)
        return ctx, token

    @classmethod
    def restore_context(cls, token):
        cls.request_context.reset(token)

    @classmethod
    def update_request_start(cls, new_request_start):
        meta = cls.request_context.get()
        # this can happen if multiple requests are sent on the wire for one logical request (e.g. scrolls)
        if "request_start" not in meta:
            meta["request_start"] = new_request_start

    @classmethod
    def update_request_end(cls, new_request_end):
        meta = cls.request_context.get()
        meta["request_end"] = new_request_end

    @classmethod
    def on_request_start(cls):
        cls.update_request_start(time.perf_counter())

    @classmethod
    def on_request_end(cls):
        cls.update_request_end(time.perf_counter())

    @classmethod
    def return_raw_response(cls):
        ctx = cls.request_context.get()
        ctx["raw_response"] = True