1 // Copyright 2009 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 /* 6 Package runtime contains operations that interact with Go's runtime system, 7 such as functions to control goroutines. It also includes the low-level type information 8 used by the reflect package; see reflect's documentation for the programmable 9 interface to the run-time type system. 10 11 # Environment Variables 12 13 The following environment variables ($name or %name%, depending on the host 14 operating system) control the run-time behavior of Go programs. The meanings 15 and use may change from release to release. 16 17 The GOGC variable sets the initial garbage collection target percentage. 18 A collection is triggered when the ratio of freshly allocated data to live data 19 remaining after the previous collection reaches this percentage. The default 20 is GOGC=100. Setting GOGC=off disables the garbage collector entirely. 21 [runtime/debug.SetGCPercent] allows changing this percentage at run time. 22 23 The GOMEMLIMIT variable sets a soft memory limit for the runtime. This memory limit 24 includes the Go heap and all other memory managed by the runtime, and excludes 25 external memory sources such as mappings of the binary itself, memory managed in 26 other languages, and memory held by the operating system on behalf of the Go 27 program. GOMEMLIMIT is a numeric value in bytes with an optional unit suffix. 28 The supported suffixes include B, KiB, MiB, GiB, and TiB. These suffixes 29 represent quantities of bytes as defined by the IEC 80000-13 standard. That is, 30 they are based on powers of two: KiB means 2^10 bytes, MiB means 2^20 bytes, 31 and so on. The default setting is math.MaxInt64, which effectively disables the 32 memory limit. [runtime/debug.SetMemoryLimit] allows changing this limit at run 33 time. 34 35 The GODEBUG variable controls debugging variables within the runtime. 36 It is a comma-separated list of name=val pairs setting these named variables: 37 38 allocfreetrace: setting allocfreetrace=1 causes every allocation to be 39 profiled and a stack trace printed on each object's allocation and free. 40 41 clobberfree: setting clobberfree=1 causes the garbage collector to 42 clobber the memory content of an object with bad content when it frees 43 the object. 44 45 cgocheck: setting cgocheck=0 disables all checks for packages 46 using cgo to incorrectly pass Go pointers to non-Go code. 47 Setting cgocheck=1 (the default) enables relatively cheap 48 checks that may miss some errors. Setting cgocheck=2 enables 49 expensive checks that should not miss any errors, but will 50 cause your program to run slower. 51 52 efence: setting efence=1 causes the allocator to run in a mode 53 where each object is allocated on a unique page and addresses are 54 never recycled. 55 56 gccheckmark: setting gccheckmark=1 enables verification of the 57 garbage collector's concurrent mark phase by performing a 58 second mark pass while the world is stopped. If the second 59 pass finds a reachable object that was not found by concurrent 60 mark, the garbage collector will panic. 61 62 gcpacertrace: setting gcpacertrace=1 causes the garbage collector to 63 print information about the internal state of the concurrent pacer. 64 65 gcshrinkstackoff: setting gcshrinkstackoff=1 disables moving goroutines 66 onto smaller stacks. In this mode, a goroutine's stack can only grow. 67 68 gcstoptheworld: setting gcstoptheworld=1 disables concurrent garbage collection, 69 making every garbage collection a stop-the-world event. Setting gcstoptheworld=2 70 also disables concurrent sweeping after the garbage collection finishes. 71 72 gctrace: setting gctrace=1 causes the garbage collector to emit a single line to standard 73 error at each collection, summarizing the amount of memory collected and the 74 length of the pause. The format of this line is subject to change. 75 Currently, it is: 76 gc # @#s #%: #+#+# ms clock, #+#/#/#+# ms cpu, #->#-># MB, # MB goal, # P 77 where the fields are as follows: 78 gc # the GC number, incremented at each GC 79 @#s time in seconds since program start 80 #% percentage of time spent in GC since program start 81 #+...+# wall-clock/CPU times for the phases of the GC 82 #->#-># MB heap size at GC start, at GC end, and live heap 83 # MB goal goal heap size 84 # MB stacks estimated scannable stack size 85 # MB globals scannable global size 86 # P number of processors used 87 The phases are stop-the-world (STW) sweep termination, concurrent 88 mark and scan, and STW mark termination. The CPU times 89 for mark/scan are broken down in to assist time (GC performed in 90 line with allocation), background GC time, and idle GC time. 91 If the line ends with "(forced)", this GC was forced by a 92 runtime.GC() call. 93 94 harddecommit: setting harddecommit=1 causes memory that is returned to the OS to 95 also have protections removed on it. This is the only mode of operation on Windows, 96 but is helpful in debugging scavenger-related issues on other platforms. Currently, 97 only supported on Linux. 98 99 inittrace: setting inittrace=1 causes the runtime to emit a single line to standard 100 error for each package with init work, summarizing the execution time and memory 101 allocation. No information is printed for inits executed as part of plugin loading 102 and for packages without both user defined and compiler generated init work. 103 The format of this line is subject to change. Currently, it is: 104 init # @#ms, # ms clock, # bytes, # allocs 105 where the fields are as follows: 106 init # the package name 107 @# ms time in milliseconds when the init started since program start 108 # clock wall-clock time for package initialization work 109 # bytes memory allocated on the heap 110 # allocs number of heap allocations 111 112 madvdontneed: setting madvdontneed=0 will use MADV_FREE 113 instead of MADV_DONTNEED on Linux when returning memory to the 114 kernel. This is more efficient, but means RSS numbers will 115 drop only when the OS is under memory pressure. 116 117 memprofilerate: setting memprofilerate=X will update the value of runtime.MemProfileRate. 118 When set to 0 memory profiling is disabled. Refer to the description of 119 MemProfileRate for the default value. 120 121 invalidptr: invalidptr=1 (the default) causes the garbage collector and stack 122 copier to crash the program if an invalid pointer value (for example, 1) 123 is found in a pointer-typed location. Setting invalidptr=0 disables this check. 124 This should only be used as a temporary workaround to diagnose buggy code. 125 The real fix is to not store integers in pointer-typed locations. 126 127 sbrk: setting sbrk=1 replaces the memory allocator and garbage collector 128 with a trivial allocator that obtains memory from the operating system and 129 never reclaims any memory. 130 131 scavtrace: setting scavtrace=1 causes the runtime to emit a single line to standard 132 error, roughly once per GC cycle, summarizing the amount of work done by the 133 scavenger as well as the total amount of memory returned to the operating system 134 and an estimate of physical memory utilization. The format of this line is subject 135 to change, but currently it is: 136 scav # KiB work, # KiB total, #% util 137 where the fields are as follows: 138 # KiB work the amount of memory returned to the OS since the last line 139 # KiB total the total amount of memory returned to the OS 140 #% util the fraction of all unscavenged memory which is in-use 141 If the line ends with "(forced)", then scavenging was forced by a 142 debug.FreeOSMemory() call. 143 144 scheddetail: setting schedtrace=X and scheddetail=1 causes the scheduler to emit 145 detailed multiline info every X milliseconds, describing state of the scheduler, 146 processors, threads and goroutines. 147 148 schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard 149 error every X milliseconds, summarizing the scheduler state. 150 151 tracebackancestors: setting tracebackancestors=N extends tracebacks with the stacks at 152 which goroutines were created, where N limits the number of ancestor goroutines to 153 report. This also extends the information returned by runtime.Stack. Ancestor's goroutine 154 IDs will refer to the ID of the goroutine at the time of creation; it's possible for this 155 ID to be reused for another goroutine. Setting N to 0 will report no ancestry information. 156 157 asyncpreemptoff: asyncpreemptoff=1 disables signal-based 158 asynchronous goroutine preemption. This makes some loops 159 non-preemptible for long periods, which may delay GC and 160 goroutine scheduling. This is useful for debugging GC issues 161 because it also disables the conservative stack scanning used 162 for asynchronously preempted goroutines. 163 164 The net and net/http packages also refer to debugging variables in GODEBUG. 165 See the documentation for those packages for details. 166 167 The GOMAXPROCS variable limits the number of operating system threads that 168 can execute user-level Go code simultaneously. There is no limit to the number of threads 169 that can be blocked in system calls on behalf of Go code; those do not count against 170 the GOMAXPROCS limit. This package's GOMAXPROCS function queries and changes 171 the limit. 172 173 The GORACE variable configures the race detector, for programs built using -race. 174 See https://golang.org/doc/articles/race_detector.html for details. 175 176 The GOTRACEBACK variable controls the amount of output generated when a Go 177 program fails due to an unrecovered panic or an unexpected runtime condition. 178 By default, a failure prints a stack trace for the current goroutine, 179 eliding functions internal to the run-time system, and then exits with exit code 2. 180 The failure prints stack traces for all goroutines if there is no current goroutine 181 or the failure is internal to the run-time. 182 GOTRACEBACK=none omits the goroutine stack traces entirely. 183 GOTRACEBACK=single (the default) behaves as described above. 184 GOTRACEBACK=all adds stack traces for all user-created goroutines. 185 GOTRACEBACK=system is like “all” but adds stack frames for run-time functions 186 and shows goroutines created internally by the run-time. 187 GOTRACEBACK=crash is like “system” but crashes in an operating system-specific 188 manner instead of exiting. For example, on Unix systems, the crash raises 189 SIGABRT to trigger a core dump. 190 For historical reasons, the GOTRACEBACK settings 0, 1, and 2 are synonyms for 191 none, all, and system, respectively. 192 The runtime/debug package's SetTraceback function allows increasing the 193 amount of output at run time, but it cannot reduce the amount below that 194 specified by the environment variable. 195 See https://golang.org/pkg/runtime/debug/#SetTraceback. 196 197 The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete 198 the set of Go environment variables. They influence the building of Go programs 199 (see https://golang.org/cmd/go and https://golang.org/pkg/go/build). 200 GOARCH, GOOS, and GOROOT are recorded at compile time and made available by 201 constants or functions in this package, but they do not influence the execution 202 of the run-time system. 203 */ 204 package runtime 205 206 import ( 207 "internal/goarch" 208 "internal/goos" 209 ) 210 211 // Caller reports file and line number information about function invocations on 212 // the calling goroutine's stack. The argument skip is the number of stack frames 213 // to ascend, with 0 identifying the caller of Caller. (For historical reasons the 214 // meaning of skip differs between Caller and Callers.) The return values report the 215 // program counter, file name, and line number within the file of the corresponding 216 // call. The boolean ok is false if it was not possible to recover the information. 217 func Caller(skip int) (pc uintptr, file string, line int, ok bool) { 218 rpc := make([]uintptr, 1) 219 n := callers(skip+1, rpc[:]) 220 if n < 1 { 221 return 222 } 223 frame, _ := CallersFrames(rpc).Next() 224 return frame.PC, frame.File, frame.Line, frame.PC != 0 225 } 226 227 // Callers fills the slice pc with the return program counters of function invocations 228 // on the calling goroutine's stack. The argument skip is the number of stack frames 229 // to skip before recording in pc, with 0 identifying the frame for Callers itself and 230 // 1 identifying the caller of Callers. 231 // It returns the number of entries written to pc. 232 // 233 // To translate these PCs into symbolic information such as function 234 // names and line numbers, use CallersFrames. CallersFrames accounts 235 // for inlined functions and adjusts the return program counters into 236 // call program counters. Iterating over the returned slice of PCs 237 // directly is discouraged, as is using FuncForPC on any of the 238 // returned PCs, since these cannot account for inlining or return 239 // program counter adjustment. 240 func Callers(skip int, pc []uintptr) int { 241 // runtime.callers uses pc.array==nil as a signal 242 // to print a stack trace. Pick off 0-length pc here 243 // so that we don't let a nil pc slice get to it. 244 if len(pc) == 0 { 245 return 0 246 } 247 return callers(skip, pc) 248 } 249 250 var defaultGOROOT string // set by cmd/link 251 252 // GOROOT returns the root of the Go tree. It uses the 253 // GOROOT environment variable, if set at process start, 254 // or else the root used during the Go build. 255 func GOROOT() string { 256 s := gogetenv("GOROOT") 257 if s != "" { 258 return s 259 } 260 return defaultGOROOT 261 } 262 263 // buildVersion is the Go tree's version string at build time. 264 // 265 // If any GOEXPERIMENTs are set to non-default values, it will include 266 // "X:<GOEXPERIMENT>". 267 // 268 // This is set by the linker. 269 // 270 // This is accessed by "go version <binary>". 271 var buildVersion string 272 273 // Version returns the Go tree's version string. 274 // It is either the commit hash and date at the time of the build or, 275 // when possible, a release tag like "go1.3". 276 func Version() string { 277 return buildVersion 278 } 279 280 // GOOS is the running program's operating system target: 281 // one of darwin, freebsd, linux, and so on. 282 // To view possible combinations of GOOS and GOARCH, run "go tool dist list". 283 const GOOS string = goos.GOOS 284 285 // GOARCH is the running program's architecture target: 286 // one of 386, amd64, arm, s390x, and so on. 287 const GOARCH string = goarch.GOARCH 288