1// Copyright 2024 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package pgo
6
7import (
8	"bufio"
9	"fmt"
10	"io"
11)
12
13// Serialization of a Profile allows go tool preprofile to construct the edge
14// map only once (rather than once per compile process). The compiler processes
15// then parse the pre-processed data directly from the serialized format.
16//
17// The format of the serialized output is as follows.
18//
19//      GO PREPROFILE V1
20//      caller_name
21//      callee_name
22//      "call site offset" "call edge weight"
23//      ...
24//      caller_name
25//      callee_name
26//      "call site offset" "call edge weight"
27//
28// Entries are sorted by "call edge weight", from highest to lowest.
29
30const serializationHeader = "GO PREPROFILE V1\n"
31
32// WriteTo writes a serialized representation of Profile to w.
33//
34// FromSerialized can parse the format back to Profile.
35//
36// WriteTo implements io.WriterTo.Write.
37func (d *Profile) WriteTo(w io.Writer) (int64, error) {
38	bw := bufio.NewWriter(w)
39
40	var written int64
41
42	// Header
43	n, err := bw.WriteString(serializationHeader)
44	written += int64(n)
45	if err != nil {
46		return written, err
47	}
48
49	for _, edge := range d.NamedEdgeMap.ByWeight {
50		weight := d.NamedEdgeMap.Weight[edge]
51
52		n, err = fmt.Fprintln(bw, edge.CallerName)
53		written += int64(n)
54		if err != nil {
55			return written, err
56		}
57
58		n, err = fmt.Fprintln(bw, edge.CalleeName)
59		written += int64(n)
60		if err != nil {
61			return written, err
62		}
63
64		n, err = fmt.Fprintf(bw, "%d %d\n", edge.CallSiteOffset, weight)
65		written += int64(n)
66		if err != nil {
67			return written, err
68		}
69	}
70
71	if err := bw.Flush(); err != nil {
72		return written, err
73	}
74
75	// No need to serialize TotalWeight, it can be trivially recomputed
76	// during parsing.
77
78	return written, nil
79}
80