[feature][bug] Add tcp transport event dispatcher unsched flag & fix RDMA event dispatcher unsched flag

[MalikHou]

Event Dispatcher Unsched Flag

What problem does this PR solve?

Problem Summary:

• Event-dispatch scheduling behavior was not unified across transports.
• RDMA used a transport-specific flag (rdma_edisp_unsched), while TCP had no unified switch.
• In RDMA path, bthread_start_urgent and bthread_start_background logic was reversed, causing behavior opposite to expected unsched semantics.
• The scheduling decision logic was duplicated in transport code, making behavior harder to reason about and test.

What is changed and the side effects?

Changed:

• Added a unified flag in dispatcher layer: event_dispatcher_edisp_unsched.
• Added EventDispatcherUnsched() helper in event_dispatcher.{h,cpp} as single source of truth.
• Updated TcpTransport::ProcessEvent and RdmaTransport::ProcessEvent to use EventDispatcherUnsched():
  • false -> bthread_start_urgent
  • true -> bthread_start_background
• Fixed RDMA bug where bthread_start_urgent and bthread_start_background branches were previously swapped.
• Deprecated rdma_edisp_unsched and kept compatibility through dispatcher-layer unified check.
• Added/updated tests in test/brpc_event_dispatcher_unittest.cpp:
  • event_dispatcher_unsched_by_unified_flag
  • event_dispatcher_unsched_by_legacy_rdma_flag (when BRPC_WITH_RDMA)
  • tcp_unsched_true_returns_before_onedge_finish
  • tcp_unsched_false_blocks_caller_when_single_worker

Effects:

• event_dispatcher_edisp_unsched=true may reduce immediate foreground switching of dispatcher path.
• rdma_edisp_unsched is deprecated.
• RDMA runtime behavior now matches intended unsched semantics after fixing the swapped urgent/background branches. Users depending on previous incorrect behavior should migrate and re-check tuning.

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Check List:

• Please make sure your changes are compilable.
• When providing us with a new feature, it is best to add related tests.
• Please follow Contributor Covenant Code of Conduct.

[Copilot]

Pull request overview

This PR unifies “unsched” scheduling behavior across TCP and RDMA transports by introducing a single dispatcher-layer flag/helper, and updates transport event processing to use that unified decision (also correcting RDMA’s urgent/background selection).

Changes:

• Added event_dispatcher_edisp_unsched and EventDispatcherUnsched() as the single source of truth for “unsched” behavior (with legacy RDMA flag OR’ed in when enabled).
• Updated TcpTransport::ProcessEvent and RdmaTransport::ProcessEvent to pick bthread_start_urgent vs bthread_start_background via EventDispatcherUnsched().
• Updated RDMA docs to describe the unified flag and deprecation of rdma_edisp_unsched.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/brpc/tcp_transport.cpp	Switches ProcessEvent scheduling decision to EventDispatcherUnsched().
src/brpc/rdma_transport.cpp	Uses unified unsched helper and fixes urgent/background selection for RDMA.
src/brpc/rdma/rdma_endpoint.h	Removes the legacy rdma_edisp_unsched declaration from an installed header.
src/brpc/rdma/rdma_endpoint.cpp	Removes the legacy rdma_edisp_unsched definition (re-homed elsewhere).
src/brpc/event_dispatcher.h	Declares new unified flag and helper (but has an incorrect semantics comment).
src/brpc/event_dispatcher.cpp	Defines new unified flag + legacy flag (deprecated) and implements EventDispatcherUnsched().
docs/en/rdma.md	Documents unified flag semantics and deprecation (contains an incorrect example).
docs/cn/rdma.md	Same as English RDMA doc update (contains an incorrect example).

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[yanglimingcn]

LGTM