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 "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 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 sort.Slice(sorted, func(i, j int) bool { return sorted[i] < sorted[j] }) 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