Merge bitcoin/bitcoin#33676: interfaces: enable cancelling running waitNext calls

dcb56fd4cb interfaces: add interruptWait method (ismaelsadeeq)

Pull request description:

  This is an attempt to fix #33575 see the issue for background and the usefulness of this feature.

  This PR uses one of the suggested approaches: adding a new `interruptWaitNext()` method to the mining interface.

  It introduces a new boolean variable, `m_interrupt_wait`, which is set to `false` when the thread starts waiting. The `interruptWaitNext()` method wakes the thread and sets `m_interrupt_wait` to `true`.
  Whenever the thread wakes up, it checks whether the wait was aborted; if so, it simply set ` m_interrupt_wait ` to false and return`nullptr`.

  This PR also adds a functional test for the new method. The test uses `asyncio` to spawn two tasks and attempts to ensure that the wait is executed before the interrupt by using an event monitor. It adds a 0.1-second buffer to ensure the wait has started executing.
  If that buffer elapses without `waitNext` executing, the test will fail because a transaction is created after the buffer.

ACKs for top commit:
  furszy:
    Code ACK dcb56fd4cb
  ryanofsky:
    Code review ACK dcb56fd4cb, just tweaking semantics slightly since last review so if an `interruptWait` call is made shortly after a `waitNext` call it will reliably cause the `waitNext` call to return right away without blocking, even if the `waitNext` call had not begun to execute or wait yet.
  Sjors:
    tACK dcb56fd4cb
  TheCharlatan:
    ACK dcb56fd4cb

Tree-SHA512: a03f049e1f303b174a9e5d125733b6583dfd8effa12e7b6c37bd9b2cff9541100f5f4514e80f89005c44a57d7e47804afe87aa5fdb6831f3b0cd9b01d83e42be

test/functional/interface_ipc.py

@@ -184,6 +184,28 @@ class IPCInterfaceTest(BitcoinTestFramework):
             template7 = await template6.result.waitNext(ctx, waitoptions)
             assert_equal(template7.to_dict(), {})
 
+            self.log.debug("interruptWait should abort the current wait")
+            wait_started = asyncio.Event()
+            async def wait_for_block():
+                new_waitoptions = self.capnp_modules['mining'].BlockWaitOptions()
+                new_waitoptions.timeout = waitoptions.timeout * 60 # 1 minute wait
+                new_waitoptions.feeThreshold = 1
+                wait_started.set()
+                return await template6.result.waitNext(ctx, new_waitoptions)
+
+            async def interrupt_wait():
+                await wait_started.wait() # Wait for confirmation wait started
+                await asyncio.sleep(0.1)  # Minimal buffer
+                template6.result.interruptWait()
+                miniwallet.send_self_transfer(fee_rate=10, from_node=self.nodes[0])
+
+            wait_task = asyncio.create_task(wait_for_block())
+            interrupt_task = asyncio.create_task(interrupt_wait())
+
+            result = await wait_task
+            await interrupt_task
+            assert_equal(result.to_dict(), {})
+
             current_block_height = self.nodes[0].getchaintips()[0]["height"]
             check_opts = self.capnp_modules['mining'].BlockCheckOptions()
             template = await mining.result.createNewBlock(opts)