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