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Fix deadlock on PluginCustomValue drop (#12418)
# Description Because the plugin interface reader thread can be responsible for sending a drop notification, it's possible for it to end up in a deadlock where it's waiting for the response to the drop notification call. I decided that the best way to address this is to just discard the response and not wait for it. It's not really important to synchronize with the response to `Dropped`, so this is probably faster anyway. cc @ayax79, this is your issue where polars is getting stuck # User-Facing Changes - A bug fix - Custom value plugin: `custom-value handle update` command # Tests + Formatting Tried to add a test with a long pipeline with a lot of drops and run it over and over to reproduce the deadlock. - 🟢 `toolkit fmt` - 🟢 `toolkit clippy` - 🟢 `toolkit test` - 🟢 `toolkit test stdlib`
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@ -93,6 +93,9 @@ impl std::fmt::Debug for PluginInterfaceState {
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struct PluginCallState {
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/// The sender back to the thread that is waiting for the plugin call response
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sender: Option<mpsc::Sender<ReceivedPluginCallMessage>>,
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/// Don't try to send the plugin call response. This is only used for `Dropped` to avoid an
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/// error
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dont_send_response: bool,
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/// Interrupt signal to be used for stream iterators
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ctrlc: Option<Arc<AtomicBool>>,
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/// Channel to receive context on to be used if needed
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@ -244,11 +247,12 @@ impl PluginInterfaceManager {
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// Remove the subscription sender, since this will be the last message.
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//
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// We can spawn a new one if we need it for engine calls.
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if e.get_mut()
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.sender
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.take()
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.and_then(|s| s.send(ReceivedPluginCallMessage::Response(response)).ok())
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.is_none()
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if !e.get().dont_send_response
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&& e.get_mut()
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.sender
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.take()
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.and_then(|s| s.send(ReceivedPluginCallMessage::Response(response)).ok())
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.is_none()
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{
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log::warn!("Received a plugin call response for id={id}, but the caller hung up");
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}
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@ -688,13 +692,18 @@ impl PluginInterface {
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}
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};
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// Don't try to send a response for a Dropped call.
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let dont_send_response =
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matches!(call, PluginCall::CustomValueOp(_, CustomValueOp::Dropped));
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// Register the subscription to the response, and the context
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self.state
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.plugin_call_subscription_sender
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.send((
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id,
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PluginCallState {
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sender: Some(tx),
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sender: Some(tx).filter(|_| !dont_send_response),
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dont_send_response,
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ctrlc,
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context_rx: Some(context_rx),
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keep_plugin_custom_values,
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@ -938,13 +947,15 @@ impl PluginInterface {
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/// Notify the plugin about a dropped custom value.
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pub fn custom_value_dropped(&self, value: PluginCustomValue) -> Result<(), ShellError> {
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// Make sure we don't block here. This can happen on the receiver thread, which would cause a deadlock. We should not try to receive the response - just let it be discarded.
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//
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// Note: the protocol is always designed to have a span with the custom value, but this
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// operation doesn't support one.
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self.custom_value_op_expecting_value(
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value.into_spanned(Span::unknown()),
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CustomValueOp::Dropped,
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)
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.map(|_| ())
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drop(self.write_plugin_call(
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PluginCall::CustomValueOp(value.into_spanned(Span::unknown()), CustomValueOp::Dropped),
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None,
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)?);
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Ok(())
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}
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}
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@ -193,6 +193,7 @@ fn fake_plugin_call(
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id,
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PluginCallState {
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sender: Some(tx),
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dont_send_response: false,
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ctrlc: None,
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context_rx: None,
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keep_plugin_custom_values: mpsc::channel(),
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@ -496,6 +497,7 @@ fn manager_handle_engine_call_after_response_received() -> Result<(), ShellError
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0,
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PluginCallState {
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sender: None,
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dont_send_response: false,
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ctrlc: None,
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context_rx: Some(context_rx),
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keep_plugin_custom_values: mpsc::channel(),
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@ -560,6 +562,7 @@ fn manager_send_plugin_call_response_removes_context_only_if_no_streams_to_read(
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n,
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PluginCallState {
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sender: None,
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dont_send_response: false,
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ctrlc: None,
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context_rx: None,
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keep_plugin_custom_values: mpsc::channel(),
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@ -594,6 +597,7 @@ fn manager_consume_stream_end_removes_context_only_if_last_stream() -> Result<()
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n,
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PluginCallState {
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sender: None,
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dont_send_response: false,
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ctrlc: None,
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context_rx: None,
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keep_plugin_custom_values: mpsc::channel(),
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