1// Copyright 2018 Google LLC
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7//      http://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14
15package profiler
16
17import (
18	"bytes"
19	"context"
20	"fmt"
21	"runtime"
22	"time"
23
24	"github.com/google/pprof/profile"
25)
26
27// heapProfile collects an in-use heap profile. The heap profiles returned by
28// the runtime also include the heap allocation metrics. We zero those out
29// since all allocations since program start are recorded, so these make the
30// profile large and there is a separate alloc profile type which shows
31// allocations from a set duration.
32func heapProfile(prof *bytes.Buffer) error {
33	p, err := goHeapProfile()
34	if err != nil {
35		return err
36	}
37	for _, s := range p.Sample {
38		s.Value[0] = 0
39		s.Value[1] = 0
40	}
41
42	// Merge profile with itself to remove samples with only zero values and
43	// reduce profile size.
44	p, err = profile.Merge([]*profile.Profile{p})
45	if err != nil {
46		return err
47	}
48	return p.Write(prof)
49}
50
51// deltaAllocProfile collects an allocation profile by gathering a heap profile,
52// sleeping for the specified duration, gathering another heap profile and
53// subtracting the initial one from that. It then drops the in-use metrics from
54// the profile. If requested, it forces the GC before taking each of the heap
55// profiles, which improves the profile accuracy (see docs in
56// https://golang.org/src/runtime/mprof.go on why).
57func deltaAllocProfile(ctx context.Context, duration time.Duration, forceGC bool, prof *bytes.Buffer) error {
58	p1, err := allocProfile(forceGC)
59	if err != nil {
60		return err
61	}
62
63	sleep(ctx, duration)
64
65	p2, err := allocProfile(forceGC)
66	if err != nil {
67		return err
68	}
69
70	p1.Scale(-1)
71	p, err := profile.Merge([]*profile.Profile{p1, p2})
72	if err != nil {
73		return err
74	}
75	p.DurationNanos = duration.Nanoseconds()
76	return p.Write(prof)
77}
78
79// allocProfile collects a single heap profile, and removes all metrics but
80// allocation metrics.
81func allocProfile(forceGC bool) (*profile.Profile, error) {
82	if forceGC {
83		runtime.GC()
84	}
85	p, err := goHeapProfile()
86	if err != nil {
87		return nil, err
88	}
89	p.SampleType = p.SampleType[:2]
90	for _, s := range p.Sample {
91		s.Value = s.Value[:2]
92	}
93	return p, nil
94}
95
96// goHeapProfile collects a heap profile. It returns an error if the metrics
97// in the collected heap profile do not match the expected metrics.
98func goHeapProfile() (*profile.Profile, error) {
99	var prof bytes.Buffer
100	if err := writeHeapProfile(&prof); err != nil {
101		return nil, fmt.Errorf("failed to write heap profile: %v", err)
102	}
103	p, err := profile.Parse(&prof)
104	if err != nil {
105		return nil, err
106	}
107	if got := len(p.SampleType); got != 4 {
108		return nil, fmt.Errorf("invalid heap profile: got %d sample types, want 4", got)
109	}
110	for i, want := range []string{"alloc_objects", "alloc_space", "inuse_objects", "inuse_space"} {
111		if got := p.SampleType[i].Type; got != want {
112			return nil, fmt.Errorf("invalid heap profile: got %q sample type at index %d, want %q", got, i, want)
113		}
114	}
115	return p, nil
116}
117