Cluster-wide semaphore using Erlang's :global module.

Creates a singleton GenServer per name that limits concurrency across all nodes in the cluster. Each semaphore name operates independently, allowing different limits for different resources.

Configuration

config :global_semaphore, :limits,
  pdf_api: 3,
  email_api: 5,
  payment_api: 2

Usage

GlobalSemaphore.with_permit(:pdf_api, fn ->
  # Only 3 concurrent executions allowed cluster-wide
end)

# Priority (lower number = higher priority, default 5)
GlobalSemaphore.with_permit({:pdf_api, 1}, fn -> ... end)   # high
GlobalSemaphore.with_permit({:pdf_api, 5}, fn -> ... end)   # normal (default)
GlobalSemaphore.with_permit({:pdf_api, 10}, fn -> ... end)  # low

Introspection

GlobalSemaphore.list_names()
#=> [:pdf_api]

GlobalSemaphore.status(:pdf_api)
#=> %{
#     name: :pdf_api,
#     max: 3,
#     holders: [%{pid: pid, node: :node1, acquired_at: ~U[...]}],
#     waiters: [%{pid: pid, node: :node2, priority: 5, enqueued_at: ~U[...]}]
#   }