garbage.go

     1  // Copyright 2013 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  
     5  package debug
     6  
     7  import (
     8  	"runtime"
     9  	"sort"
    10  	"time"
    11  )
    12  
    13  // GCStats collect information about recent garbage collections.
    14  type GCStats struct {
    15  	LastGC         time.Time       // time of last collection
    16  	NumGC          int64           // number of garbage collections
    17  	PauseTotal     time.Duration   // total pause for all collections
    18  	Pause          []time.Duration // pause history, most recent first
    19  	PauseEnd       []time.Time     // pause end times history, most recent first
    20  	PauseQuantiles []time.Duration
    21  }
    22  
    23  // ReadGCStats reads statistics about garbage collection into stats.
    24  // The number of entries in the pause history is system-dependent;
    25  // stats.Pause slice will be reused if large enough, reallocated otherwise.
    26  // ReadGCStats may use the full capacity of the stats.Pause slice.
    27  // If stats.PauseQuantiles is non-empty, ReadGCStats fills it with quantiles
    28  // summarizing the distribution of pause time. For example, if
    29  // len(stats.PauseQuantiles) is 5, it will be filled with the minimum,
    30  // 25%, 50%, 75%, and maximum pause times.
    31  func ReadGCStats(stats *GCStats) {
    32  	// Create a buffer with space for at least two copies of the
    33  	// pause history tracked by the runtime. One will be returned
    34  	// to the caller and the other will be used as transfer buffer
    35  	// for end times history and as a temporary buffer for
    36  	// computing quantiles.
    37  	const maxPause = len(((*runtime.MemStats)(nil)).PauseNs)
    38  	if cap(stats.Pause) < 2*maxPause+3 {
    39  		stats.Pause = make([]time.Duration, 2*maxPause+3)
    40  	}
    41  
    42  	// readGCStats fills in the pause and end times histories (up to
    43  	// maxPause entries) and then three more: Unix ns time of last GC,
    44  	// number of GC, and total pause time in nanoseconds. Here we
    45  	// depend on the fact that time.Duration's native unit is
    46  	// nanoseconds, so the pauses and the total pause time do not need
    47  	// any conversion.
    48  	readGCStats(&stats.Pause)
    49  	n := len(stats.Pause) - 3
    50  	stats.LastGC = time.Unix(0, int64(stats.Pause[n]))
    51  	stats.NumGC = int64(stats.Pause[n+1])
    52  	stats.PauseTotal = stats.Pause[n+2]
    53  	n /= 2 // buffer holds pauses and end times
    54  	stats.Pause = stats.Pause[:n]
    55  
    56  	if cap(stats.PauseEnd) < maxPause {
    57  		stats.PauseEnd = make([]time.Time, 0, maxPause)
    58  	}
    59  	stats.PauseEnd = stats.PauseEnd[:0]
    60  	for _, ns := range stats.Pause[n : n+n] {
    61  		stats.PauseEnd = append(stats.PauseEnd, time.Unix(0, int64(ns)))
    62  	}
    63  
    64  	if len(stats.PauseQuantiles) > 0 {
    65  		if n == 0 {
    66  			for i := range stats.PauseQuantiles {
    67  				stats.PauseQuantiles[i] = 0
    68  			}
    69  		} else {
    70  			// There's room for a second copy of the data in stats.Pause.
    71  			// See the allocation at the top of the function.
    72  			sorted := stats.Pause[n : n+n]
    73  			copy(sorted, stats.Pause)
    74  			sort.Slice(sorted, func(i, j int) bool { return sorted[i] < sorted[j] })
    75  			nq := len(stats.PauseQuantiles) - 1
    76  			for i := 0; i < nq; i++ {
    77  				stats.PauseQuantiles[i] = sorted[len(sorted)*i/nq]
    78  			}
    79  			stats.PauseQuantiles[nq] = sorted[len(sorted)-1]
    80  		}
    81  	}
    82  }
    83  
    84  // SetGCPercent sets the garbage collection target percentage:
    85  // a collection is triggered when the ratio of freshly allocated data
    86  // to live data remaining after the previous collection reaches this percentage.
    87  // SetGCPercent returns the previous setting.
    88  // The initial setting is the value of the GOGC environment variable
    89  // at startup, or 100 if the variable is not set.
    90  // A negative percentage disables garbage collection.
    91  func SetGCPercent(percent int) int {
    92  	return int(setGCPercent(int32(percent)))
    93  }
    94  
    95  // FreeOSMemory forces a garbage collection followed by an
    96  // attempt to return as much memory to the operating system
    97  // as possible. (Even if this is not called, the runtime gradually
    98  // returns memory to the operating system in a background task.)
    99  func FreeOSMemory() {
   100  	freeOSMemory()
   101  }
   102  
   103  // SetMaxStack sets the maximum amount of memory that
   104  // can be used by a single goroutine stack.
   105  // If any goroutine exceeds this limit while growing its stack,
   106  // the program crashes.
   107  // SetMaxStack returns the previous setting.
   108  // The initial setting is 1 GB on 64-bit systems, 250 MB on 32-bit systems.
   109  // There may be a system-imposed maximum stack limit regardless
   110  // of the value provided to SetMaxStack.
   111  //
   112  // SetMaxStack is useful mainly for limiting the damage done by
   113  // goroutines that enter an infinite recursion. It only limits future
   114  // stack growth.
   115  func SetMaxStack(bytes int) int {
   116  	return setMaxStack(bytes)
   117  }
   118  
   119  // SetMaxThreads sets the maximum number of operating system
   120  // threads that the Go program can use. If it attempts to use more than
   121  // this many, the program crashes.
   122  // SetMaxThreads returns the previous setting.
   123  // The initial setting is 10,000 threads.
   124  //
   125  // The limit controls the number of operating system threads, not the number
   126  // of goroutines. A Go program creates a new thread only when a goroutine
   127  // is ready to run but all the existing threads are blocked in system calls, cgo calls,
   128  // or are locked to other goroutines due to use of runtime.LockOSThread.
   129  //
   130  // SetMaxThreads is useful mainly for limiting the damage done by
   131  // programs that create an unbounded number of threads. The idea is
   132  // to take down the program before it takes down the operating system.
   133  func SetMaxThreads(threads int) int {
   134  	return setMaxThreads(threads)
   135  }
   136  
   137  // SetPanicOnFault controls the runtime's behavior when a program faults
   138  // at an unexpected (non-nil) address. Such faults are typically caused by
   139  // bugs such as runtime memory corruption, so the default response is to crash
   140  // the program. Programs working with memory-mapped files or unsafe
   141  // manipulation of memory may cause faults at non-nil addresses in less
   142  // dramatic situations; SetPanicOnFault allows such programs to request
   143  // that the runtime trigger only a panic, not a crash.
   144  // The runtime.Error that the runtime panics with may have an additional method:
   145  //     Addr() uintptr
   146  // If that method exists, it returns the memory address which triggered the fault.
   147  // The results of Addr are best-effort and the veracity of the result
   148  // may depend on the platform.
   149  // SetPanicOnFault applies only to the current goroutine.
   150  // It returns the previous setting.
   151  func SetPanicOnFault(enabled bool) bool {
   152  	return setPanicOnFault(enabled)
   153  }
   154  
   155  // WriteHeapDump writes a description of the heap and the objects in
   156  // it to the given file descriptor.
   157  //
   158  // WriteHeapDump suspends the execution of all goroutines until the heap
   159  // dump is completely written.  Thus, the file descriptor must not be
   160  // connected to a pipe or socket whose other end is in the same Go
   161  // process; instead, use a temporary file or network socket.
   162  //
   163  // The heap dump format is defined at https://golang.org/s/go15heapdump.
   164  func WriteHeapDump(fd uintptr)
   165  
   166  // SetTraceback sets the amount of detail printed by the runtime in
   167  // the traceback it prints before exiting due to an unrecovered panic
   168  // or an internal runtime error.
   169  // The level argument takes the same values as the GOTRACEBACK
   170  // environment variable. For example, SetTraceback("all") ensure
   171  // that the program prints all goroutines when it crashes.
   172  // See the package runtime documentation for details.
   173  // If SetTraceback is called with a level lower than that of the
   174  // environment variable, the call is ignored.
   175  func SetTraceback(level string)
   176
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