console-api,console-subscriber,tokio-console: implement stack traces for tasks

The task detail view of console now shows the tree of extant
consequences stemming from that task; i.e., which spans are
open beneath the task. The leaves of the task, in a sense,
reflect what the task is busy doing at that moment.

Author: jswrenn

Cargo.lock

@@ -78,6 +78,8 @@ message Span {
     repeated Field fields = 3;
     // Timestamp for the span.
     google.protobuf.Timestamp at = 4;
+    // An Id that uniquely identifies this span's parent (if any).
+    optional SpanId parent_id = 5;
 }
 
 // Any new metadata that was registered since the last update.
@@ -197,4 +199,4 @@ message Attribute {
     // Some values carry a unit of measurement. For example, a duration
     // carries an associated unit of time, such as "ms" for milliseconds.
     optional string unit = 2;
-}
+}

console-api/proto/common.proto

@@ -0,0 +1,53 @@
+syntax = "proto3";
+
+package rs.tokio.console.consequences;
+
+import "common.proto";
+
+message Causality {
+    oneof update {
+        Extant extant = 1;
+        OpenDirect open_direct = 2;
+        NewIndirect new_indirect = 3;
+        CloseDirect close_direct = 4;
+        CloseIndirect close_indirect = 5;
+        CloseCyclic close_cyclic = 6;
+    }
+}
+
+message Span {
+    common.SpanId span_id = 1;
+    common.MetaId metadata_id = 2;
+}
+
+message Extant {
+    Span cause = 1;
+    repeated Span direct_consequences = 2;
+    repeated Span indirect_consequences = 3;
+}
+
+message OpenDirect {
+    Span cause = 1;
+    Span direct_consequences = 2;
+}
+
+message NewIndirect {
+    Span cause = 1;
+    Span indirect_consequences = 3;
+}
+
+message CloseDirect {
+    Span span = 1;
+    optional Span direct_cause = 2;
+}
+
+message CloseIndirect {
+    Span span = 1;
+    repeated Span indirect_causes = 3;
+}
+
+message CloseCyclic {
+    Span span = 1;
+    optional Span direct_cause = 2;
+    repeated Span indirect_causes = 3;
+}

console-api/proto/consequences.proto

@@ -4,6 +4,7 @@ package rs.tokio.console.tasks;
 
 import "google/protobuf/timestamp.proto";
 import "google/protobuf/duration.proto";
+import "consequences.proto";
 import "common.proto";
 
 // A task state update.
@@ -49,6 +50,9 @@ message TaskDetails {
 
     // HdrHistogram.rs `Histogram` serialized to binary in the V2 format
     optional bytes poll_times_histogram = 3;
+
+    // What the task is currently busy doing.
+    repeated consequences.Causality causality = 4;
 }
 
 // Data recorded when a new task is spawned.

console-api/proto/tasks.proto

@@ -0,0 +1 @@
+include!("generated/rs.tokio.console.consequences.rs");

console-api/src/consequences.rs

@@ -106,6 +106,9 @@ pub struct Span {
     /// Timestamp for the span.
     #[prost(message, optional, tag="4")]
     pub at: ::core::option::Option<::prost_types::Timestamp>,
+    /// An Id that uniquely identifies this span's parent (if any).
+    #[prost(message, optional, tag="5")]
+    pub parent_id: ::core::option::Option<SpanId>,
 }
 /// Any new metadata that was registered since the last update.
 #[derive(Clone, PartialEq, ::prost::Message)]