Source file src/runtime/extern.go
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 harddecommit: setting harddecommit=1 causes memory that is returned to the OS to 82 also have protections removed on it. This is the only mode of operation on Windows, 83 but is helpful in debugging scavenger-related issues on other platforms. Currently, 84 only supported on Linux. 85 86 inittrace: setting inittrace=1 causes the runtime to emit a single line to standard 87 error for each package with init work, summarizing the execution time and memory 88 allocation. No information is printed for inits executed as part of plugin loading 89 and for packages without both user defined and compiler generated init work. 90 The format of this line is subject to change. Currently, it is: 91 init # @#ms, # ms clock, # bytes, # allocs 92 where the fields are as follows: 93 init # the package name 94 @# ms time in milliseconds when the init started since program start 95 # clock wall-clock time for package initialization work 96 # bytes memory allocated on the heap 97 # allocs number of heap allocations 98 99 madvdontneed: setting madvdontneed=0 will use MADV_FREE 100 instead of MADV_DONTNEED on Linux when returning memory to the 101 kernel. This is more efficient, but means RSS numbers will 102 drop only when the OS is under memory pressure. 103 104 memprofilerate: setting memprofilerate=X will update the value of runtime.MemProfileRate. 105 When set to 0 memory profiling is disabled. Refer to the description of 106 MemProfileRate for the default value. 107 108 invalidptr: invalidptr=1 (the default) causes the garbage collector and stack 109 copier to crash the program if an invalid pointer value (for example, 1) 110 is found in a pointer-typed location. Setting invalidptr=0 disables this check. 111 This should only be used as a temporary workaround to diagnose buggy code. 112 The real fix is to not store integers in pointer-typed locations. 113 114 sbrk: setting sbrk=1 replaces the memory allocator and garbage collector 115 with a trivial allocator that obtains memory from the operating system and 116 never reclaims any memory. 117 118 scavtrace: setting scavtrace=1 causes the runtime to emit a single line to standard 119 error, roughly once per GC cycle, summarizing the amount of work done by the 120 scavenger as well as the total amount of memory returned to the operating system 121 and an estimate of physical memory utilization. The format of this line is subject 122 to change, but currently it is: 123 scav # # KiB work, # KiB total, #% util 124 where the fields are as follows: 125 scav # the scavenge cycle number 126 # KiB work the amount of memory returned to the OS since the last line 127 # KiB total the total amount of memory returned to the OS 128 #% util the fraction of all unscavenged memory which is in-use 129 If the line ends with "(forced)", then scavenging was forced by a 130 debug.FreeOSMemory() call. 131 132 scheddetail: setting schedtrace=X and scheddetail=1 causes the scheduler to emit 133 detailed multiline info every X milliseconds, describing state of the scheduler, 134 processors, threads and goroutines. 135 136 schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard 137 error every X milliseconds, summarizing the scheduler state. 138 139 tracebackancestors: setting tracebackancestors=N extends tracebacks with the stacks at 140 which goroutines were created, where N limits the number of ancestor goroutines to 141 report. This also extends the information returned by runtime.Stack. Ancestor's goroutine 142 IDs will refer to the ID of the goroutine at the time of creation; it's possible for this 143 ID to be reused for another goroutine. Setting N to 0 will report no ancestry information. 144 145 asyncpreemptoff: asyncpreemptoff=1 disables signal-based 146 asynchronous goroutine preemption. This makes some loops 147 non-preemptible for long periods, which may delay GC and 148 goroutine scheduling. This is useful for debugging GC issues 149 because it also disables the conservative stack scanning used 150 for asynchronously preempted goroutines. 151 152 The net and net/http packages also refer to debugging variables in GODEBUG. 153 See the documentation for those packages for details. 154 155 The GOMAXPROCS variable limits the number of operating system threads that 156 can execute user-level Go code simultaneously. There is no limit to the number of threads 157 that can be blocked in system calls on behalf of Go code; those do not count against 158 the GOMAXPROCS limit. This package's GOMAXPROCS function queries and changes 159 the limit. 160 161 The GORACE variable configures the race detector, for programs built using -race. 162 See https://golang.org/doc/articles/race_detector.html for details. 163 164 The GOTRACEBACK variable controls the amount of output generated when a Go 165 program fails due to an unrecovered panic or an unexpected runtime condition. 166 By default, a failure prints a stack trace for the current goroutine, 167 eliding functions internal to the run-time system, and then exits with exit code 2. 168 The failure prints stack traces for all goroutines if there is no current goroutine 169 or the failure is internal to the run-time. 170 GOTRACEBACK=none omits the goroutine stack traces entirely. 171 GOTRACEBACK=single (the default) behaves as described above. 172 GOTRACEBACK=all adds stack traces for all user-created goroutines. 173 GOTRACEBACK=system is like ``all'' but adds stack frames for run-time functions 174 and shows goroutines created internally by the run-time. 175 GOTRACEBACK=crash is like ``system'' but crashes in an operating system-specific 176 manner instead of exiting. For example, on Unix systems, the crash raises 177 SIGABRT to trigger a core dump. 178 For historical reasons, the GOTRACEBACK settings 0, 1, and 2 are synonyms for 179 none, all, and system, respectively. 180 The runtime/debug package's SetTraceback function allows increasing the 181 amount of output at run time, but it cannot reduce the amount below that 182 specified by the environment variable. 183 See https://golang.org/pkg/runtime/debug/#SetTraceback. 184 185 The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete 186 the set of Go environment variables. They influence the building of Go programs 187 (see https://golang.org/cmd/go and https://golang.org/pkg/go/build). 188 GOARCH, GOOS, and GOROOT are recorded at compile time and made available by 189 constants or functions in this package, but they do not influence the execution 190 of the run-time system. 191 */ 192 package runtime 193 194 import ( 195 "internal/goarch" 196 "internal/goos" 197 ) 198 199 // Caller reports file and line number information about function invocations on 200 // the calling goroutine's stack. The argument skip is the number of stack frames 201 // to ascend, with 0 identifying the caller of Caller. (For historical reasons the 202 // meaning of skip differs between Caller and Callers.) The return values report the 203 // program counter, file name, and line number within the file of the corresponding 204 // call. The boolean ok is false if it was not possible to recover the information. 205 func Caller(skip int) (pc uintptr, file string, line int, ok bool) { 206 rpc := make([]uintptr, 1) 207 n := callers(skip+1, rpc[:]) 208 if n < 1 { 209 return 210 } 211 frame, _ := CallersFrames(rpc).Next() 212 return frame.PC, frame.File, frame.Line, frame.PC != 0 213 } 214 215 // Callers fills the slice pc with the return program counters of function invocations 216 // on the calling goroutine's stack. The argument skip is the number of stack frames 217 // to skip before recording in pc, with 0 identifying the frame for Callers itself and 218 // 1 identifying the caller of Callers. 219 // It returns the number of entries written to pc. 220 // 221 // To translate these PCs into symbolic information such as function 222 // names and line numbers, use CallersFrames. CallersFrames accounts 223 // for inlined functions and adjusts the return program counters into 224 // call program counters. Iterating over the returned slice of PCs 225 // directly is discouraged, as is using FuncForPC on any of the 226 // returned PCs, since these cannot account for inlining or return 227 // program counter adjustment. 228 func Callers(skip int, pc []uintptr) int { 229 // runtime.callers uses pc.array==nil as a signal 230 // to print a stack trace. Pick off 0-length pc here 231 // so that we don't let a nil pc slice get to it. 232 if len(pc) == 0 { 233 return 0 234 } 235 return callers(skip, pc) 236 } 237 238 var defaultGOROOT string // set by cmd/link 239 240 // GOROOT returns the root of the Go tree. It uses the 241 // GOROOT environment variable, if set at process start, 242 // or else the root used during the Go build. 243 func GOROOT() string { 244 s := gogetenv("GOROOT") 245 if s != "" { 246 return s 247 } 248 return defaultGOROOT 249 } 250 251 // buildVersion is the Go tree's version string at build time. 252 // 253 // If any GOEXPERIMENTs are set to non-default values, it will include 254 // "X:<GOEXPERIMENT>". 255 // 256 // This is set by the linker. 257 // 258 // This is accessed by "go version <binary>". 259 var buildVersion string 260 261 // Version returns the Go tree's version string. 262 // It is either the commit hash and date at the time of the build or, 263 // when possible, a release tag like "go1.3". 264 func Version() string { 265 return buildVersion 266 } 267 268 // GOOS is the running program's operating system target: 269 // one of darwin, freebsd, linux, and so on. 270 // To view possible combinations of GOOS and GOARCH, run "go tool dist list". 271 const GOOS string = goos.GOOS 272 273 // GOARCH is the running program's architecture target: 274 // one of 386, amd64, arm, s390x, and so on. 275 const GOARCH string = goarch.GOARCH 276