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Source file src/runtime/debug/garbage.go

Documentation: runtime/debug

  // Copyright 2013 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 debug
  import (
  // GCStats collect information about recent garbage collections.
  type GCStats struct {
  	LastGC         time.Time       // time of last collection
  	NumGC          int64           // number of garbage collections
  	PauseTotal     time.Duration   // total pause for all collections
  	Pause          []time.Duration // pause history, most recent first
  	PauseEnd       []time.Time     // pause end times history, most recent first
  	PauseQuantiles []time.Duration
  // ReadGCStats reads statistics about garbage collection into stats.
  // The number of entries in the pause history is system-dependent;
  // stats.Pause slice will be reused if large enough, reallocated otherwise.
  // ReadGCStats may use the full capacity of the stats.Pause slice.
  // If stats.PauseQuantiles is non-empty, ReadGCStats fills it with quantiles
  // summarizing the distribution of pause time. For example, if
  // len(stats.PauseQuantiles) is 5, it will be filled with the minimum,
  // 25%, 50%, 75%, and maximum pause times.
  func ReadGCStats(stats *GCStats) {
  	// Create a buffer with space for at least two copies of the
  	// pause history tracked by the runtime. One will be returned
  	// to the caller and the other will be used as transfer buffer
  	// for end times history and as a temporary buffer for
  	// computing quantiles.
  	const maxPause = len(((*runtime.MemStats)(nil)).PauseNs)
  	if cap(stats.Pause) < 2*maxPause+3 {
  		stats.Pause = make([]time.Duration, 2*maxPause+3)
  	// readGCStats fills in the pause and end times histories (up to
  	// maxPause entries) and then three more: Unix ns time of last GC,
  	// number of GC, and total pause time in nanoseconds. Here we
  	// depend on the fact that time.Duration's native unit is
  	// nanoseconds, so the pauses and the total pause time do not need
  	// any conversion.
  	n := len(stats.Pause) - 3
  	stats.LastGC = time.Unix(0, int64(stats.Pause[n]))
  	stats.NumGC = int64(stats.Pause[n+1])
  	stats.PauseTotal = stats.Pause[n+2]
  	n /= 2 // buffer holds pauses and end times
  	stats.Pause = stats.Pause[:n]
  	if cap(stats.PauseEnd) < maxPause {
  		stats.PauseEnd = make([]time.Time, 0, maxPause)
  	stats.PauseEnd = stats.PauseEnd[:0]
  	for _, ns := range stats.Pause[n : n+n] {
  		stats.PauseEnd = append(stats.PauseEnd, time.Unix(0, int64(ns)))
  	if len(stats.PauseQuantiles) > 0 {
  		if n == 0 {
  			for i := range stats.PauseQuantiles {
  				stats.PauseQuantiles[i] = 0
  		} else {
  			// There's room for a second copy of the data in stats.Pause.
  			// See the allocation at the top of the function.
  			sorted := stats.Pause[n : n+n]
  			copy(sorted, stats.Pause)
  			sort.Slice(sorted, func(i, j int) bool { return sorted[i] < sorted[j] })
  			nq := len(stats.PauseQuantiles) - 1
  			for i := 0; i < nq; i++ {
  				stats.PauseQuantiles[i] = sorted[len(sorted)*i/nq]
  			stats.PauseQuantiles[nq] = sorted[len(sorted)-1]
  // SetGCPercent sets the garbage collection target percentage:
  // a collection is triggered when the ratio of freshly allocated data
  // to live data remaining after the previous collection reaches this percentage.
  // SetGCPercent returns the previous setting.
  // The initial setting is the value of the GOGC environment variable
  // at startup, or 100 if the variable is not set.
  // A negative percentage disables garbage collection.
  func SetGCPercent(percent int) int {
  	return int(setGCPercent(int32(percent)))
  // FreeOSMemory forces a garbage collection followed by an
  // attempt to return as much memory to the operating system
  // as possible. (Even if this is not called, the runtime gradually
  // returns memory to the operating system in a background task.)
  func FreeOSMemory() {
  // SetMaxStack sets the maximum amount of memory that
  // can be used by a single goroutine stack.
  // If any goroutine exceeds this limit while growing its stack,
  // the program crashes.
  // SetMaxStack returns the previous setting.
  // The initial setting is 1 GB on 64-bit systems, 250 MB on 32-bit systems.
  // SetMaxStack is useful mainly for limiting the damage done by
  // goroutines that enter an infinite recursion. It only limits future
  // stack growth.
  func SetMaxStack(bytes int) int {
  	return setMaxStack(bytes)
  // SetMaxThreads sets the maximum number of operating system
  // threads that the Go program can use. If it attempts to use more than
  // this many, the program crashes.
  // SetMaxThreads returns the previous setting.
  // The initial setting is 10,000 threads.
  // The limit controls the number of operating system threads, not the number
  // of goroutines. A Go program creates a new thread only when a goroutine
  // is ready to run but all the existing threads are blocked in system calls, cgo calls,
  // or are locked to other goroutines due to use of runtime.LockOSThread.
  // SetMaxThreads is useful mainly for limiting the damage done by
  // programs that create an unbounded number of threads. The idea is
  // to take down the program before it takes down the operating system.
  func SetMaxThreads(threads int) int {
  	return setMaxThreads(threads)
  // SetPanicOnFault controls the runtime's behavior when a program faults
  // at an unexpected (non-nil) address. Such faults are typically caused by
  // bugs such as runtime memory corruption, so the default response is to crash
  // the program. Programs working with memory-mapped files or unsafe
  // manipulation of memory may cause faults at non-nil addresses in less
  // dramatic situations; SetPanicOnFault allows such programs to request
  // that the runtime trigger only a panic, not a crash.
  // SetPanicOnFault applies only to the current goroutine.
  // It returns the previous setting.
  func SetPanicOnFault(enabled bool) bool {
  	return setPanicOnFault(enabled)
  // WriteHeapDump writes a description of the heap and the objects in
  // it to the given file descriptor.
  // WriteHeapDump suspends the execution of all goroutines until the heap
  // dump is completely written.  Thus, the file descriptor must not be
  // connected to a pipe or socket whose other end is in the same Go
  // process; instead, use a temporary file or network socket.
  // The heap dump format is defined at https://golang.org/s/go15heapdump.
  func WriteHeapDump(fd uintptr)
  // SetTraceback sets the amount of detail printed by the runtime in
  // the traceback it prints before exiting due to an unrecovered panic
  // or an internal runtime error.
  // The level argument takes the same values as the GOTRACEBACK
  // environment variable. For example, SetTraceback("all") ensure
  // that the program prints all goroutines when it crashes.
  // See the package runtime documentation for details.
  // If SetTraceback is called with a level lower than that of the
  // environment variable, the call is ignored.
  func SetTraceback(level string)

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