internal/trace: interpret string ID arguments for experimental events

Currently one of the reasons experimental events are tricky to use is
because:
- There's no way to take advantage of the existing infrastructure, like
  strings and stacks, and
- There's no way to attach arbitrary data to an event (except through
  strings, possibly).

Fix this by abstracting away the raw arguments in an ExperimentalEvent
and requiring access to the arguments via a new method, ArgValue. This
returns a Value, which gives us an opportunity to construct a typed
value for the raw argument dynamically, and a way to access existing
tables. The type of the argument is deduced from conventions for the
argument's name. This seems more than sufficient for experimental
events.

To make this work, we also need to add a "string" variant to the Value
type. This may be a little confusing since they're primarily used for
metrics, but one could imagine other scenarios in which this is useful,
such as including build information in the trace as a metric, so I think
this is fine.

This change also updates the Value API to accomodate a String method for
use with things that expect a fmt.Stringer, which means renaming the
value assertion methods to have a "To" prefix.

Change-Id: I43a2334f6cd306122c5b94641a6252ca4258b39f
Reviewed-on: https://go-review.googlesource.com/c/go/+/645135
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>

diff --git a/src/cmd/trace/gen.go b/src/cmd/trace/gen.go
index 03ee5037e9f779c68e01e3977c18747f5a70f523..6e4d82799e581db7a1566d9b50791a7aeb3b408d 100644 (file)
--- a/src/cmd/trace/gen.go
+++ b/src/cmd/trace/gen.go
@@ -282,11 +282,11 @@ func (g *globalMetricGenerator) GlobalMetric(ctx *traceContext, ev *trace.Event)
        m := ev.Metric()
        switch m.Name {
        case "/memory/classes/heap/objects:bytes":
-               ctx.HeapAlloc(ctx.elapsed(ev.Time()), m.Value.Uint64())
+               ctx.HeapAlloc(ctx.elapsed(ev.Time()), m.Value.ToUint64())
        case "/gc/heap/goal:bytes":
-               ctx.HeapGoal(ctx.elapsed(ev.Time()), m.Value.Uint64())
+               ctx.HeapGoal(ctx.elapsed(ev.Time()), m.Value.ToUint64())
        case "/sched/gomaxprocs:threads":
-               ctx.Gomaxprocs(m.Value.Uint64())
+               ctx.Gomaxprocs(m.Value.ToUint64())
        }
 }
 

diff --git a/src/internal/trace/event.go b/src/internal/trace/event.go
index ebf8aaa97790baed89f4a509a0ae501c4eaf80a3..896ab7f73a1f1cbd2ce3e13613c6ebe3d3ada6dd 100644 (file)
--- a/src/internal/trace/event.go
+++ b/src/internal/trace/event.go
@@ -315,12 +315,25 @@ type ExperimentalEvent struct {
        // Experiment is the name of the experiment this event is a part of.
        Experiment string
 
-       // ArgNames is the names of the event's arguments in order.
-       // This may refer to a globally shared slice. Copy before mutating.
-       ArgNames []string
+       // Args lists the names of the event's arguments in order.
+       Args []string
 
-       // Args contains the event's arguments.
-       Args []uint64
+       // argValues contains the raw integer arguments which are interpreted
+       // by ArgValue using table.
+       table     *evTable
+       argValues []uint64
+}
+
+// ArgValue returns a typed Value for the i'th argument in the experimental event.
+func (e ExperimentalEvent) ArgValue(i int) Value {
+       if i < 0 || i >= len(e.Args) {
+               panic(fmt.Sprintf("experimental event argument index %d out of bounds [0, %d)", i, len(e.Args)))
+       }
+       if strings.HasSuffix(e.Args[i], "string") {
+               s := e.table.strings.mustGet(stringID(e.argValues[i]))
+               return stringValue(s)
+       }
+       return uint64Value(e.argValues[i])
 }
 
 // ExperimentalBatch represents a packet of unparsed data along with metadata about that packet.
@@ -421,13 +434,13 @@ func (e Event) Metric() Metric {
        switch e.base.typ {
        case tracev2.EvProcsChange:
                m.Name = "/sched/gomaxprocs:threads"
-               m.Value = Value{kind: ValueUint64, scalar: e.base.args[0]}
+               m.Value = uint64Value(e.base.args[0])
        case tracev2.EvHeapAlloc:
                m.Name = "/memory/classes/heap/objects:bytes"
-               m.Value = Value{kind: ValueUint64, scalar: e.base.args[0]}
+               m.Value = uint64Value(e.base.args[0])
        case tracev2.EvHeapGoal:
                m.Name = "/gc/heap/goal:bytes"
-               m.Value = Value{kind: ValueUint64, scalar: e.base.args[0]}
+               m.Value = uint64Value(e.base.args[0])
        default:
                panic(fmt.Sprintf("internal error: unexpected wire-format event type for Metric kind: %d", e.base.typ))
        }
@@ -503,11 +516,11 @@ func (e Event) RangeAttributes() []RangeAttribute {
        return []RangeAttribute{
                {
                        Name:  "bytes swept",
-                       Value: Value{kind: ValueUint64, scalar: e.base.args[0]},
+                       Value: uint64Value(e.base.args[0]),
                },
                {
                        Name:  "bytes reclaimed",
-                       Value: Value{kind: ValueUint64, scalar: e.base.args[1]},
+                       Value: uint64Value(e.base.args[1]),
                },
        }
 }
@@ -687,8 +700,9 @@ func (e Event) Experimental() ExperimentalEvent {
        return ExperimentalEvent{
                Name:       spec.Name,
                Experiment: tracev2.Experiments()[spec.Experiment],
-               ArgNames:   argNames,
-               Args:       e.base.args[:len(argNames)],
+               Args:       argNames,
+               table:      e.table,
+               argValues:  e.base.args[:len(argNames)],
        }
 }
 
@@ -773,7 +787,7 @@ func (e Event) String() string {
        switch kind := e.Kind(); kind {
        case EventMetric:
                m := e.Metric()
-               fmt.Fprintf(&sb, " Name=%q Value=%s", m.Name, valueAsString(m.Value))
+               fmt.Fprintf(&sb, " Name=%q Value=%s", m.Name, m.Value)
        case EventLabel:
                l := e.Label()
                fmt.Fprintf(&sb, " Label=%q Resource=%s", l.Label, l.Resource)
@@ -786,7 +800,7 @@ func (e Event) String() string {
                                if i != 0 {
                                        fmt.Fprintf(&sb, " ")
                                }
-                               fmt.Fprintf(&sb, "%q=%s", attr.Name, valueAsString(attr.Value))
+                               fmt.Fprintf(&sb, "%q=%s", attr.Name, attr.Value)
                        }
                        fmt.Fprintf(&sb, "]")
                }
@@ -822,7 +836,14 @@ func (e Event) String() string {
                }
        case EventExperimental:
                r := e.Experimental()
-               fmt.Fprintf(&sb, " Name=%s ArgNames=%v Args=%v", r.Name, r.ArgNames, r.Args)
+               fmt.Fprintf(&sb, " Name=%s Args=[", r.Name)
+               for i, arg := range r.Args {
+                       if i != 0 {
+                               fmt.Fprintf(&sb, ", ")
+                       }
+                       fmt.Fprintf(&sb, "%s=%s", arg, r.ArgValue(i).String())
+               }
+               fmt.Fprintf(&sb, "]")
        }
        if stk := e.Stack(); stk != NoStack {
                fmt.Fprintln(&sb)

diff --git a/src/internal/trace/gc.go b/src/internal/trace/gc.go
index 46890e784df24cf84e7584926c26c031ae0a5e53..f5e8fe79f293be13c2640872d01a270325917b53 100644 (file)
--- a/src/internal/trace/gc.go
+++ b/src/internal/trace/gc.go
@@ -103,7 +103,7 @@ func MutatorUtilizationV2(events []Event, flags UtilFlags) [][]MutatorUtil {
                        if m.Name != "/sched/gomaxprocs:threads" {
                                break
                        }
-                       gomaxprocs := int(m.Value.Uint64())
+                       gomaxprocs := int(m.Value.ToUint64())
                        if len(ps) > gomaxprocs {
                                if flags&UtilPerProc != 0 {
                                        // End each P's series.

diff --git a/src/internal/trace/testtrace/validation.go b/src/internal/trace/testtrace/validation.go
index 3d12f75c499ff6ab4359c3de4fabe103da847b4e..f61f7a3ffa603161b682922829c2c873d0b07436 100644 (file)
--- a/src/internal/trace/testtrace/validation.go
+++ b/src/internal/trace/testtrace/validation.go
@@ -91,7 +91,7 @@ func (v *Validator) Event(ev trace.Event) error {
                switch m.Value.Kind() {
                case trace.ValueUint64:
                        // Just make sure it doesn't panic.
-                       _ = m.Value.Uint64()
+                       _ = m.Value.ToUint64()
                }
        case trace.EventLabel:
                l := ev.Label()

diff --git a/src/internal/trace/tracev2/spec.go b/src/internal/trace/tracev2/spec.go
index af92865781741da911bf686605491b0f00a426c4..6e54c399f49ddf4abc84d438cd9f94a0306f2e20 100644 (file)
--- a/src/internal/trace/tracev2/spec.go
+++ b/src/internal/trace/tracev2/spec.go
@@ -19,7 +19,9 @@ type EventSpec struct {
        // Its length determines the number of arguments an event has.
        //
        // Argument names follow a certain structure and this structure
-       // is relied on by the testing framework to type-check arguments.
+       // is relied on by the testing framework to type-check arguments
+       // and to produce Values for experimental events.
+       //
        // The structure is:
        //
        //     (?P<name>[A-Za-z]+)(_(?P<type>[A-Za-z]+))?

diff --git a/src/internal/trace/value.go b/src/internal/trace/value.go
index bd2cba7878355d6ce45f0bba1a85cfeabee702a9..bf396b6a9ee3943ac05e67678546ad5843cebc36 100644 (file)
--- a/src/internal/trace/value.go
+++ b/src/internal/trace/value.go
@@ -4,12 +4,16 @@
 
 package trace
 
-import "fmt"
+import (
+       "fmt"
+       "unsafe"
+)
 
 // Value is a dynamically-typed value obtained from a trace.
 type Value struct {
-       kind   ValueKind
-       scalar uint64
+       kind    ValueKind
+       pointer unsafe.Pointer
+       scalar  uint64
 }
 
 // ValueKind is the type of a dynamically-typed value from a trace.
@@ -18,6 +22,7 @@ type ValueKind uint8
 const (
        ValueBad ValueKind = iota
        ValueUint64
+       ValueString
 )
 
 // Kind returns the ValueKind of the value.
@@ -30,24 +35,41 @@ func (v Value) Kind() ValueKind {
        return v.kind
 }
 
-// Uint64 returns the uint64 value for a MetricSampleUint64.
+// ToUint64 returns the uint64 value for a ValueUint64.
 //
-// Panics if this metric sample's Kind is not MetricSampleUint64.
-func (v Value) Uint64() uint64 {
+// Panics if this Value's Kind is not ValueUint64.
+func (v Value) ToUint64() uint64 {
        if v.kind != ValueUint64 {
-               panic("Uint64 called on Value of a different Kind")
+               panic("ToUint64 called on Value of a different Kind")
        }
        return v.scalar
 }
 
-// valueAsString produces a debug string value.
+// ToString returns the uint64 value for a ValueString.
 //
-// This isn't just Value.String because we may want to use that to store
-// string values in the future.
-func valueAsString(v Value) string {
+// Panics if this Value's Kind is not ValueString.
+func (v Value) ToString() string {
+       if v.kind != ValueString {
+               panic("ToString called on Value of a different Kind")
+       }
+       return unsafe.String((*byte)(v.pointer), int(v.scalar))
+}
+
+func uint64Value(x uint64) Value {
+       return Value{kind: ValueUint64, scalar: x}
+}
+
+func stringValue(s string) Value {
+       return Value{kind: ValueString, scalar: uint64(len(s)), pointer: unsafe.Pointer(unsafe.StringData(s))}
+}
+
+// String returns the string representation of the value.
+func (v Value) String() string {
        switch v.Kind() {
        case ValueUint64:
-               return fmt.Sprintf("Uint64(%d)", v.scalar)
+               return fmt.Sprintf("Value{Uint64(%d)}", v.ToUint64())
+       case ValueString:
+               return fmt.Sprintf("Value{String(%s)}", v.ToString())
        }
-       return "Bad"
+       return "Value{Bad}"
 }