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// Package sync is an extension of the stdlib "sync" package. It has extra
// functionality that helps debug the use of synchronization primitives. The
// package should be importable in place of "sync". The extra functionality
// can be enabled by calling Enable() or passing a non-empty PPROF_SYNC
// environment variable to the process.
//
// Several profiles are exposed on the default HTTP muxer (and to
// "/debug/pprof" when "net/http/pprof" is imported by the process).
// "lockHolders" lists the stack traces of goroutines that called Mutex.Lock
// that haven't subsequently been Unlocked. "lockBlockers" contains goroutines
// that are waiting to obtain locks. "/debug/lockTimes" or PrintLockTimes()
// shows the longest time a lock is held for each stack trace.
//
// Note that currently RWMutex is treated like a Mutex when the package is
// enabled.
package sync
import (
"fmt"
"io"
"net/http"
"os"
"runtime/pprof"
"strings"
"sync"
"text/tabwriter"
"github.com/anacrolix/missinggo/v2"
)
var (
// Protects initialization and enabling of the package.
enableMu sync.Mutex
// Whether shared locks must be handled as exclusive locks.
noSharedLocking = false
contentionOn = false
lockTimesOn = false
// Current lock holders.
lockHolders *pprof.Profile
// Those blocked on acquiring a lock.
lockBlockers *pprof.Profile
)
// Writes out the longest time a Mutex remains locked for each stack trace
// that locks a Mutex.
func PrintLockTimes(w io.Writer) {
lockTimes := sortedLockTimes()
tw := tabwriter.NewWriter(w, 1, 8, 1, '\t', 0)
defer tw.Flush()
w = tw
for _, elem := range lockTimes {
fmt.Fprintf(w, "%s (%s * %d [%s, %s])\n", elem.Total, elem.MeanTime(), elem.Count, elem.Min, elem.Max)
missinggo.WriteStack(w, elem.stack[:])
}
}
func Enable() {
EnableContention()
EnableLockTimes()
}
func EnableContention() {
lockHolders = pprof.NewProfile("lockHolders")
lockBlockers = pprof.NewProfile("lockBlockers")
noSharedLocking = true
contentionOn = true
}
func EnableLockTimes() {
lockStatsByStack = make(map[lockStackKey]lockStats)
http.DefaultServeMux.HandleFunc("/debug/lockTimes", func(w http.ResponseWriter, r *http.Request) {
PrintLockTimes(w)
})
noSharedLocking = true
lockTimesOn = true
}
func init() {
env := os.Getenv("PPROF_SYNC")
all := true
if strings.Contains(env, "times") {
EnableLockTimes()
all = false
}
if strings.Contains(env, "contention") {
EnableContention()
all = false
}
if all && env != "" {
Enable()
}
}
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