Class: MCP::Server::PendingResponse

Inherits:
Object
  • Object
show all
Defined in:
lib/mcp/server/pending_response.rb

Overview

A one-shot, timeout-aware handoff between the thread awaiting a server-to-client response and whichever thread resolves it (the client's response, a cancellation, or session teardown).

Queue#pop only accepts a timeout: on Ruby 3.2 and later, and this gem supports 2.7, so the wait is expressed with a ConditionVariable. The push/pop names mirror the Queue this replaces, keeping the resolving call sites unchanged.

First writer wins: a second push is ignored, so a cancellation that races a real response cannot overwrite it. pop returns the pushed value, or the on_timeout result when the deadline passes with nothing pushed.

Instance Method Summary collapse

Constructor Details

#initialize ⇒ PendingResponse

Returns a new instance of PendingResponse.



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# File 'lib/mcp/server/pending_response.rb', line 16

def initialize
  @mutex = Mutex.new
  @condition = ConditionVariable.new
  @delivered = false
  @value = nil
end

Instance Method Details

#pop(timeout:) ⇒ Object

Blocks until a value is pushed or timeout seconds elapse, and yields to the caller on expiry so it can decide what a timeout means. ConditionVariable#wait can return spuriously, so the deadline is re-checked against the monotonic clock.

The expiry block runs after the lock is released: it typically cancels the request, which resolves this same object, and Ruby's Mutex is not reentrant.



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# File 'lib/mcp/server/pending_response.rb', line 40

def pop(timeout:)
  deadline = Process.clock_gettime(Process::CLOCK_MONOTONIC) + timeout
  expired = false

  value = @mutex.synchronize do
    until @delivered
      remaining = deadline - Process.clock_gettime(Process::CLOCK_MONOTONIC)
      if remaining <= 0
        expired = true
        break
      end

      @condition.wait(@mutex, remaining)
    end

    @value
  end

  expired ? yield : value
end

#push(value) ⇒ Object

Resolves the wait. Ignored when a value was already delivered.



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# File 'lib/mcp/server/pending_response.rb', line 24

def push(value)
  @mutex.synchronize do
    next if @delivered

    @delivered = true
    @value = value
    @condition.broadcast
  end
end