Source file src/runtime/debug/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  	"slices"
    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  			clear(stats.PauseQuantiles)
    67  		} else {
    68  			// There's room for a second copy of the data in stats.Pause.
    69  			// See the allocation at the top of the function.
    70  			sorted := stats.Pause[n : n+n]
    71  			copy(sorted, stats.Pause)
    72  			slices.Sort(sorted)
    73  			nq := len(stats.PauseQuantiles) - 1
    74  			for i := 0; i < nq; i++ {
    75  				stats.PauseQuantiles[i] = sorted[len(sorted)*i/nq]
    76  			}
    77  			stats.PauseQuantiles[nq] = sorted[len(sorted)-1]
    78  		}
    79  	}
    80  }
    81  
    82  // SetGCPercent sets the garbage collection target percentage:
    83  // a collection is triggered when the ratio of freshly allocated data
    84  // to live data remaining after the previous collection reaches this percentage.
    85  // SetGCPercent returns the previous setting.
    86  // The initial setting is the value of the GOGC environment variable
    87  // at startup, or 100 if the variable is not set.
    88  // This setting may be effectively reduced in order to maintain a memory
    89  // limit.
    90  // A negative percentage effectively disables garbage collection, unless
    91  // the memory limit is reached.
    92  // See SetMemoryLimit for more details.
    93  func SetGCPercent(percent int) int {
    94  	return int(setGCPercent(int32(percent)))
    95  }
    96  
    97  // FreeOSMemory forces a garbage collection followed by an
    98  // attempt to return as much memory to the operating system
    99  // as possible. (Even if this is not called, the runtime gradually
   100  // returns memory to the operating system in a background task.)
   101  func FreeOSMemory() {
   102  	freeOSMemory()
   103  }
   104  
   105  // SetMaxStack sets the maximum amount of memory that
   106  // can be used by a single goroutine stack.
   107  // If any goroutine exceeds this limit while growing its stack,
   108  // the program crashes.
   109  // SetMaxStack returns the previous setting.
   110  // The initial setting is 1 GB on 64-bit systems, 250 MB on 32-bit systems.
   111  // There may be a system-imposed maximum stack limit regardless
   112  // of the value provided to SetMaxStack.
   113  //
   114  // SetMaxStack is useful mainly for limiting the damage done by
   115  // goroutines that enter an infinite recursion. It only limits future
   116  // stack growth.
   117  func SetMaxStack(bytes int) int {
   118  	return setMaxStack(bytes)
   119  }
   120  
   121  // SetMaxThreads sets the maximum number of operating system
   122  // threads that the Go program can use. If it attempts to use more than
   123  // this many, the program crashes.
   124  // SetMaxThreads returns the previous setting.
   125  // The initial setting is 10,000 threads.
   126  //
   127  // The limit controls the number of operating system threads, not the number
   128  // of goroutines. A Go program creates a new thread only when a goroutine
   129  // is ready to run but all the existing threads are blocked in system calls, cgo calls,
   130  // or are locked to other goroutines due to use of runtime.LockOSThread.
   131  //
   132  // SetMaxThreads is useful mainly for limiting the damage done by
   133  // programs that create an unbounded number of threads. The idea is
   134  // to take down the program before it takes down the operating system.
   135  func SetMaxThreads(threads int) int {
   136  	return setMaxThreads(threads)
   137  }
   138  
   139  // SetPanicOnFault controls the runtime's behavior when a program faults
   140  // at an unexpected (non-nil) address. Such faults are typically caused by
   141  // bugs such as runtime memory corruption, so the default response is to crash
   142  // the program. Programs working with memory-mapped files or unsafe
   143  // manipulation of memory may cause faults at non-nil addresses in less
   144  // dramatic situations; SetPanicOnFault allows such programs to request
   145  // that the runtime trigger only a panic, not a crash.
   146  // The runtime.Error that the runtime panics with may have an additional method:
   147  //
   148  //	Addr() uintptr
   149  //
   150  // If that method exists, it returns the memory address which triggered the fault.
   151  // The results of Addr are best-effort and the veracity of the result
   152  // may depend on the platform.
   153  // SetPanicOnFault applies only to the current goroutine.
   154  // It returns the previous setting.
   155  func SetPanicOnFault(enabled bool) bool {
   156  	return setPanicOnFault(enabled)
   157  }
   158  
   159  // WriteHeapDump writes a description of the heap and the objects in
   160  // it to the given file descriptor.
   161  //
   162  // WriteHeapDump suspends the execution of all goroutines until the heap
   163  // dump is completely written.  Thus, the file descriptor must not be
   164  // connected to a pipe or socket whose other end is in the same Go
   165  // process; instead, use a temporary file or network socket.
   166  //
   167  // The heap dump format is defined at https://golang.org/s/go15heapdump.
   168  func WriteHeapDump(fd uintptr)
   169  
   170  // SetTraceback sets the amount of detail printed by the runtime in
   171  // the traceback it prints before exiting due to an unrecovered panic
   172  // or an internal runtime error.
   173  // The level argument takes the same values as the GOTRACEBACK
   174  // environment variable. For example, SetTraceback("all") ensure
   175  // that the program prints all goroutines when it crashes.
   176  // See the package runtime documentation for details.
   177  // If SetTraceback is called with a level lower than that of the
   178  // environment variable, the call is ignored.
   179  func SetTraceback(level string)
   180  
   181  // SetMemoryLimit provides the runtime with a soft memory limit.
   182  //
   183  // The runtime undertakes several processes to try to respect this
   184  // memory limit, including adjustments to the frequency of garbage
   185  // collections and returning memory to the underlying system more
   186  // aggressively. This limit will be respected even if GOGC=off (or,
   187  // if SetGCPercent(-1) is executed).
   188  //
   189  // The input limit is provided as bytes, and includes all memory
   190  // mapped, managed, and not released by the Go runtime. Notably, it
   191  // does not account for space used by the Go binary and memory
   192  // external to Go, such as memory managed by the underlying system
   193  // on behalf of the process, or memory managed by non-Go code inside
   194  // the same process. Examples of excluded memory sources include: OS
   195  // kernel memory held on behalf of the process, memory allocated by
   196  // C code, and memory mapped by syscall.Mmap (because it is not
   197  // managed by the Go runtime).
   198  //
   199  // More specifically, the following expression accurately reflects
   200  // the value the runtime attempts to maintain as the limit:
   201  //
   202  //	runtime.MemStats.Sys - runtime.MemStats.HeapReleased
   203  //
   204  // or in terms of the runtime/metrics package:
   205  //
   206  //	/memory/classes/total:bytes - /memory/classes/heap/released:bytes
   207  //
   208  // A zero limit or a limit that's lower than the amount of memory
   209  // used by the Go runtime may cause the garbage collector to run
   210  // nearly continuously. However, the application may still make
   211  // progress.
   212  //
   213  // The memory limit is always respected by the Go runtime, so to
   214  // effectively disable this behavior, set the limit very high.
   215  // [math.MaxInt64] is the canonical value for disabling the limit,
   216  // but values much greater than the available memory on the underlying
   217  // system work just as well.
   218  //
   219  // See https://go.dev/doc/gc-guide for a detailed guide explaining
   220  // the soft memory limit in more detail, as well as a variety of common
   221  // use-cases and scenarios.
   222  //
   223  // The initial setting is math.MaxInt64 unless the GOMEMLIMIT
   224  // environment variable is set, in which case it provides the initial
   225  // setting. GOMEMLIMIT is a numeric value in bytes with an optional
   226  // unit suffix. The supported suffixes include B, KiB, MiB, GiB, and
   227  // TiB. These suffixes represent quantities of bytes as defined by
   228  // the IEC 80000-13 standard. That is, they are based on powers of
   229  // two: KiB means 2^10 bytes, MiB means 2^20 bytes, and so on.
   230  //
   231  // SetMemoryLimit returns the previously set memory limit.
   232  // A negative input does not adjust the limit, and allows for
   233  // retrieval of the currently set memory limit.
   234  func SetMemoryLimit(limit int64) int64 {
   235  	return setMemoryLimit(limit)
   236  }
   237  

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