Release list fixes & broader use

[zenhack]

This patch fixes a bug I caught in releaseList: because .Release() is defined on a non-pointer receiver, doing defer rl.Release() dereferences rl up front, so future calls to .Add() don't actaully affect the slice that gets passed to .Release(). So this patch makes the receiver a pointer to avoid this.

It also expands the use of defer for releaseLists (the bug was caught in the process of doing so).

Finally, I made a simplification to the locking in handleFinish, to use defer for the unlock. Maybe this should have been its own PR, but... oh well.

[lthibault]

=== RUN   TestRecvDisembargo
Error:     level0_test.go:2124: conn error: rpc: incoming disembargo: answer ID 55 has not sent return
Error:     level0_test.go:2124: conn error: incoming return: send finish: build message: rpc: connection closed
Error:     level0_test.go:2124: conn error: send return: rpc: connection closed
Error:     level0_test.go:2124: conn error: send return: rpc: connection closed
Error:     level1_test.go:767: don't know how to handle abort; skipping
Error:     level1_test.go:674: recvMessage(ctx, p2): transport: stream transport: receive: io: read/write on closed pipe
--- FAIL: TestRecvDisembargo (0.09s)

I think this is a new one.

[lthibault]

On second thought, this looks like #377.

[lthibault]

==================
WARNING: DATA RACE
Write at 0x00c000000088 by goroutine 4399:
  capnproto.org/go/capnp/v3.alloc()
      /home/runner/work/go-capnproto2/go-capnproto2/message.go:356 +0x1d2
  capnproto.org/go/capnp/v3.NewCompositeList()
      /home/runner/work/go-capnproto2/go-capnproto2/list.go:62 +0xe4
  capnproto.org/go/capnp/v3/std/capnp/rpc.NewCapDescriptor_List()
      /home/runner/work/go-capnproto2/go-capnproto2/std/capnp/rpc/rpc.capnp.go:2406 +0xce
  capnproto.org/go/capnp/v3/std/capnp/rpc.Payload.NewCapTable()
      /home/runner/work/go-capnproto2/go-capnproto2/std/capnp/rpc/rpc.capnp.go:2179 +0x84
  capnproto.org/go/capnp/v3/rpc.(*Conn).fillPayloadCapTable()
      /home/runner/work/go-capnproto2/go-capnproto2/rpc/export.go:183 +0x1fa
  capnproto.org/go/capnp/v3/rpc.(*answer).sendReturn()
      /home/runner/work/go-capnproto2/go-capnproto2/rpc/answer.go:228 +0x174
  capnproto.org/go/capnp/v3/rpc.(*answer).Return()
      /home/runner/work/go-capnproto2/go-capnproto2/rpc/answer.go:197 +0x11d
  capnproto.org/go/capnp/v3/server.(*Server).handleCall()
      /home/runner/work/go-capnproto2/go-capnproto2/server/server.go:214 +0x281
  capnproto.org/go/capnp/v3/server.(*Server).handleCalls.func2()
      /home/runner/work/go-capnproto2/go-capnproto2/server/server.go:182 +0x84
  capnproto.org/go/capnp/v3/server.(*Server).handleCalls()
      /home/runner/work/go-capnproto2/go-capnproto2/server/server.go:183 +0x1c4
  capnproto.org/go/capnp/v3/server.New.func1()
      /home/runner/work/go-capnproto2/go-capnproto2/server/server.go:122 +0x58

Previous read at 0x00c000000088 by goroutine 4405:
  capnproto.org/go/capnp/v3.(*Segment).slice()
      /home/runner/work/go-capnproto2/go-capnproto2/segment.go:49 +0x5d
  capnproto.org/go/capnp/v3.(*Segment).readUint64()
      /home/runner/work/go-capnproto2/go-capnproto2/segment.go:65 +0x51
  capnproto.org/go/capnp/v3.(*Segment).readRawPointer()
      /home/runner/work/go-capnproto2/go-capnproto2/segment.go:69 +0x50
  capnproto.org/go/capnp/v3.(*Segment).resolveFarPointer()
      /home/runner/work/go-capnproto2/go-capnproto2/segment.go:235 +0x4f
  capnproto.org/go/capnp/v3.(*Segment).readPtr()
      /home/runner/work/go-capnproto2/go-capnproto2/segment.go:116 +0x75
  capnproto.org/go/capnp/v3.Struct.Ptr()
      /home/runner/work/go-capnproto2/go-capnproto2/struct.go:109 +0x119
  capnproto.org/go/capnp/v3.Transform()
      /home/runner/work/go-capnproto2/go-capnproto2/answer.go:580 +0x2ed
  capnproto.org/go/capnp/v3.resolution.ptr()
      /home/runner/work/go-capnproto2/go-capnproto2/answer.go:606 +0xfc
  capnproto.org/go/capnp/v3.resolution.client()
      /home/runner/work/go-capnproto2/go-capnproto2/answer.go:615 +0x96
  capnproto.org/go/capnp/v3.(*Answer).PipelineRecv()
      /home/runner/work/go-capnproto2/go-capnproto2/answer.go:393 +0x413
  capnproto.org/go/capnp/v3.(*Answer).PipelineRecv-fm()
      <autogenerated>:1 +0xc7
  capnproto.org/go/capnp/v3/server.queueCaller.PipelineRecv()
      /home/runner/work/go-capnproto2/go-capnproto2/server/answer.go:161 +0x2e2
  capnproto.org/go/capnp/v3/server.(*answerQueue).PipelineRecv()
      /home/runner/work/go-capnproto2/go-capnproto2/server/answer.go:136 +0xc9
  capnproto.org/go/capnp/v3/rpc.(*Conn).handleCall()
      /home/runner/work/go-capnproto2/go-capnproto2/rpc/rpc.go:837 +0x1f32
  capnproto.org/go/capnp/v3/rpc.(*Conn).receive()
      /home/runner/work/go-capnproto2/go-capnproto2/rpc/rpc.go:543 +0x644
  capnproto.org/go/capnp/v3/rpc.(*Conn).receive-fm()
      <autogenerated>:1 +0x39
  capnproto.org/go/capnp/v3/rpc.(*Conn).backgroundTask.func1()
      /home/runner/work/go-capnproto2/go-capnproto2/rpc/rpc.go:206 +0x92
  golang.org/x/sync/errgroup.(*Group).Go.func1()
      /home/runner/go/pkg/mod/golang.org/x/sync@v0.0.0-20201020160332-67f06af15bc9/errgroup/errgroup.go:57 +0x91

Goroutine 4399 (running) created at:
  capnproto.org/go/capnp/v3/server.New()
      /home/runner/work/go-capnproto2/go-capnproto2/server/server.go:122 +0x544
  capnproto.org/go/capnp/v3/rpc/internal/testcapnp.CapArgsTest_NewServer()
      /home/runner/work/go-capnproto2/go-capnproto2/rpc/internal/testcapnp/test.capnp.go:654 +0xc9
  capnproto.org/go/capnp/v3/rpc/internal/testcapnp.CapArgsTest_ServerToClient()
      /home/runner/work/go-capnproto2/go-capnproto2/rpc/internal/testcapnp/test.capnp.go:660 +0x36
  capnproto.org/go/capnp/v3/rpc.TestCallReceiverAnswerRpc()
      /home/runner/work/go-capnproto2/go-capnproto2/rpc/receiveranswer_test.go:108 +0x28b
  testing.tRunner()
      /opt/hostedtoolcache/go/1.19.4/x64/src/testing/testing.go:1446 +0x216
  testing.(*T).Run.func1()
      /opt/hostedtoolcache/go/1.19.4/x64/src/testing/testing.go:1493 +0x47

Goroutine 4405 (running) created at:
  golang.org/x/sync/errgroup.(*Group).Go()
      /home/runner/go/pkg/mod/golang.org/x/sync@v0.0.0-20201020160332-67f06af15bc9/errgroup/errgroup.go:54 +0xee
  capnproto.org/go/capnp/v3/rpc.NewConn()
      /home/runner/work/go-capnproto2/go-capnproto2/rpc/rpc.go:172 +0x744
  capnproto.org/go/capnp/v3/rpc.TestCallReceiverAnswerRpc()
      /home/runner/work/go-capnproto2/go-capnproto2/rpc/receiveranswer_test.go:105 +0x2d3
  testing.tRunner()
      /opt/hostedtoolcache/go/1.19.4/x64/src/testing/testing.go:1446 +0x216
  testing.(*T).Run.func1()
      /opt/hostedtoolcache/go/1.19.4/x64/src/testing/testing.go:1493 +0x47
==================

Is this one new?

[zenhack]

No, that's the one that was re-intrroduced when we backed out the fix for #349