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// Copyright 2010 The Go Authors.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package pprof writes runtime profiling data in the format expected
// by the pprof visualization tool.
// For more information about pprof, see
// http://code.google.com/p/google-perftools/.
package pprof

import (
        "bufio"
        "fmt"
        "io"
        "runtime"
        "sync"
)

// BUG(rsc): CPU profiling is broken on OS X, due to an Apple kernel bug.
// For details, see http://code.google.com/p/go/source/detail?r=35b716c94225.

// WriteHeapProfile writes a pprof-formatted heap profile to w.
// If a write to w returns an error, WriteHeapProfile returns that error.
// Otherwise, WriteHeapProfile returns nil.
func WriteHeapProfile(w io.Writer) error {
        // Find out how many records there are (MemProfile(nil, false)),
        // allocate that many records, and get the data.
        // There's a race—more records might be added between
        // the two calls—so allocate a few extra records for safety
        // and also try again if we're very unlucky.
        // The loop should only execute one iteration in the common case.
        var p []runtime.MemProfileRecord
        n, ok := runtime.MemProfile(nil, false)
        for {
                // Allocate room for a slightly bigger profile,
                // in case a few more entries have been added
                // since the call to MemProfile.
                p = make([]runtime.MemProfileRecord, n+50)
                n, ok = runtime.MemProfile(p, false)
                if ok {
                        p = p[0:n]
                        break
                }
                // Profile grew; try again.
        }

        var total runtime.MemProfileRecord
        for i := range p {
                r := &p[i]
                total.AllocBytes += r.AllocBytes
                total.AllocObjects += r.AllocObjects
                total.FreeBytes += r.FreeBytes
                total.FreeObjects += r.FreeObjects
        }

        // Technically the rate is MemProfileRate not 2*MemProfileRate,
        // but early versions of the C++ heap profiler reported 2*MemProfileRate,
        // so that's what pprof has come to expect.
        b := bufio.NewWriter(w)
        fmt.Fprintf(b, "heap profile: %d: %d [%d: %d] @ heap/%d\n",
                total.InUseObjects(), total.InUseBytes(),
                total.AllocObjects, total.AllocBytes,
                2*runtime.MemProfileRate)

        for i := range p {
                r := &p[i]
                fmt.Fprintf(b, "%d: %d [%d: %d] @",
                        r.InUseObjects(), r.InUseBytes(),
                        r.AllocObjects, r.AllocBytes)
                for _, pc := range r.Stack() {
                        fmt.Fprintf(b, " %#x", pc)
                }
                fmt.Fprintf(b, "\n")
        }

        // Print memstats information too.
        // Pprof will ignore, but useful for people.
        s := new(runtime.MemStats)
        runtime.ReadMemStats(s)
        fmt.Fprintf(b, "\n# runtime.MemStats\n")
        fmt.Fprintf(b, "# Alloc = %d\n", s.Alloc)
        fmt.Fprintf(b, "# TotalAlloc = %d\n", s.TotalAlloc)
        fmt.Fprintf(b, "# Sys = %d\n", s.Sys)
        fmt.Fprintf(b, "# Lookups = %d\n", s.Lookups)
        fmt.Fprintf(b, "# Mallocs = %d\n", s.Mallocs)

        fmt.Fprintf(b, "# HeapAlloc = %d\n", s.HeapAlloc)
        fmt.Fprintf(b, "# HeapSys = %d\n", s.HeapSys)
        fmt.Fprintf(b, "# HeapIdle = %d\n", s.HeapIdle)
        fmt.Fprintf(b, "# HeapInuse = %d\n", s.HeapInuse)

        fmt.Fprintf(b, "# Stack = %d / %d\n", s.StackInuse, s.StackSys)
        fmt.Fprintf(b, "# MSpan = %d / %d\n", s.MSpanInuse, s.MSpanSys)
        fmt.Fprintf(b, "# MCache = %d / %d\n", s.MCacheInuse, s.MCacheSys)
        fmt.Fprintf(b, "# BuckHashSys = %d\n", s.BuckHashSys)

        fmt.Fprintf(b, "# NextGC = %d\n", s.NextGC)
        fmt.Fprintf(b, "# PauseNs = %d\n", s.PauseNs)
        fmt.Fprintf(b, "# NumGC = %d\n", s.NumGC)
        fmt.Fprintf(b, "# EnableGC = %v\n", s.EnableGC)
        fmt.Fprintf(b, "# DebugGC = %v\n", s.DebugGC)

        fmt.Fprintf(b, "# BySize = Size * (Active = Mallocs - Frees)\n")
        fmt.Fprintf(b, "# (Excluding large blocks.)\n")
        for _, t := range s.BySize {
                if t.Mallocs > 0 {
                        fmt.Fprintf(b, "#   %d * (%d = %d - %d)\n", t.Size, t.Mallocs-t.Frees, t.Mallocs, t.Frees)
                }
        }
        return b.Flush()
}

var cpu struct {
        sync.Mutex
        profiling bool
        done      chan bool
}

// StartCPUProfile enables CPU profiling for the current process.
// While profiling, the profile will be buffered and written to w.
// StartCPUProfile returns an error if profiling is already enabled.
func StartCPUProfile(w io.Writer) error {
        // The runtime routines allow a variable profiling rate,
        // but in practice operating systems cannot trigger signals
        // at more than about 500 Hz, and our processing of the
        // signal is not cheap (mostly getting the stack trace).
        // 100 Hz is a reasonable choice: it is frequent enough to
        // produce useful data, rare enough not to bog down the
        // system, and a nice round number to make it easy to
        // convert sample counts to seconds.  Instead of requiring
        // each client to specify the frequency, we hard code it.
        const hz = 100

        // Avoid queueing behind StopCPUProfile.
        // Could use TryLock instead if we had it.
        if cpu.profiling {
                return fmt.Errorf("cpu profiling already in use")
        }

        cpu.Lock()
        defer cpu.Unlock()
        if cpu.done == nil {
                cpu.done = make(chan bool)
        }
        // Double-check.
        if cpu.profiling {
                return fmt.Errorf("cpu profiling already in use")
        }
        cpu.profiling = true
        runtime.SetCPUProfileRate(hz)
        go profileWriter(w)
        return nil
}

func profileWriter(w io.Writer) {
        for {
                data := runtime.CPUProfile()
                if data == nil {
                        break
                }
                w.Write(data)
        }
        cpu.done <- true
}

// StopCPUProfile stops the current CPU profile, if any.
// StopCPUProfile only returns after all the writes for the
// profile have completed.
func StopCPUProfile() {
        cpu.Lock()
        defer cpu.Unlock()

        if !cpu.profiling {
                return
        }
        cpu.profiling = false
        runtime.SetCPUProfileRate(0)
        <-cpu.done
}