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/* 6Package runtime contains operations that interact with Go's runtime system, 7such as functions to control goroutines. It also includes the low-level type information 8used by the reflect package; see reflect's documentation for the programmable 9interface to the run-time type system. 10 11Environment Variables 12 13The following environment variables ($name or %name%, depending on the host 14operating system) control the run-time behavior of Go programs. The meanings 15and use may change from release to release. 16 17The GOGC variable sets the initial garbage collection target percentage. 18A collection is triggered when the ratio of freshly allocated data to live data 19remaining after the previous collection reaches this percentage. The default 20is GOGC=100. Setting GOGC=off disables the garbage collector entirely. 21The runtime/debug package's SetGCPercent function allows changing this 22percentage at run time. See https://golang.org/pkg/runtime/debug/#SetGCPercent. 23 24The GODEBUG variable controls debugging variables within the runtime. 25It 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 madvdontneed: setting madvdontneed=1 will use MADV_DONTNEED 82 instead of MADV_FREE on Linux when returning memory to the 83 kernel. This is less efficient, but causes RSS numbers to drop 84 more quickly. 85 86 memprofilerate: setting memprofilerate=X will update the value of runtime.MemProfileRate. 87 When set to 0 memory profiling is disabled. Refer to the description of 88 MemProfileRate for the default value. 89 90 memprofilerate: setting memprofilerate=X changes the setting for 91 runtime.MemProfileRate. Refer to the description of this variable for how 92 it is used and its default value. 93 94 sbrk: setting sbrk=1 replaces the memory allocator and garbage collector 95 with a trivial allocator that obtains memory from the operating system and 96 never reclaims any memory. 97 98 scavenge: scavenge=1 enables debugging mode of heap scavenger. 99 100 scavtrace: setting scavtrace=1 causes the runtime to emit a single line to standard 101 error, roughly once per GC cycle, summarizing the amount of work done by the 102 scavenger as well as the total amount of memory returned to the operating system 103 and an estimate of physical memory utilization. The format of this line is subject 104 to change, but currently it is: 105 scav # KiB work, # KiB total, #% util 106 where the fields are as follows: 107 # KiB work the amount of memory returned to the OS since the last scav line 108 # KiB total how much of the heap at this point in time has been released to the OS 109 #% util the fraction of all unscavenged memory which is in-use 110 If the line ends with "(forced)", then scavenging was forced by a 111 debug.FreeOSMemory() call. 112 113 scheddetail: setting schedtrace=X and scheddetail=1 causes the scheduler to emit 114 detailed multiline info every X milliseconds, describing state of the scheduler, 115 processors, threads and goroutines. 116 117 schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard 118 error every X milliseconds, summarizing the scheduler state. 119 120 tracebackancestors: setting tracebackancestors=N extends tracebacks with the stacks at 121 which goroutines were created, where N limits the number of ancestor goroutines to 122 report. This also extends the information returned by runtime.Stack. Ancestor's goroutine 123 IDs will refer to the ID of the goroutine at the time of creation; it's possible for this 124 ID to be reused for another goroutine. Setting N to 0 will report no ancestry information. 125 126 asyncpreemptoff: asyncpreemptoff=1 disables signal-based 127 asynchronous goroutine preemption. This makes some loops 128 non-preemptible for long periods, which may delay GC and 129 goroutine scheduling. This is useful for debugging GC issues 130 because it also disables the conservative stack scanning used 131 for asynchronously preempted goroutines. 132 133The net, net/http, and crypto/tls packages also refer to debugging variables in GODEBUG. 134See the documentation for those packages for details. 135 136The GOMAXPROCS variable limits the number of operating system threads that 137can execute user-level Go code simultaneously. There is no limit to the number of threads 138that can be blocked in system calls on behalf of Go code; those do not count against 139the GOMAXPROCS limit. This package's GOMAXPROCS function queries and changes 140the limit. 141 142The GORACE variable configures the race detector, for programs built using -race. 143See https://golang.org/doc/articles/race_detector.html for details. 144 145The GOTRACEBACK variable controls the amount of output generated when a Go 146program fails due to an unrecovered panic or an unexpected runtime condition. 147By default, a failure prints a stack trace for the current goroutine, 148eliding functions internal to the run-time system, and then exits with exit code 2. 149The failure prints stack traces for all goroutines if there is no current goroutine 150or the failure is internal to the run-time. 151GOTRACEBACK=none omits the goroutine stack traces entirely. 152GOTRACEBACK=single (the default) behaves as described above. 153GOTRACEBACK=all adds stack traces for all user-created goroutines. 154GOTRACEBACK=system is like ``all'' but adds stack frames for run-time functions 155and shows goroutines created internally by the run-time. 156GOTRACEBACK=crash is like ``system'' but crashes in an operating system-specific 157manner instead of exiting. For example, on Unix systems, the crash raises 158SIGABRT to trigger a core dump. 159For historical reasons, the GOTRACEBACK settings 0, 1, and 2 are synonyms for 160none, all, and system, respectively. 161The runtime/debug package's SetTraceback function allows increasing the 162amount of output at run time, but it cannot reduce the amount below that 163specified by the environment variable. 164See https://golang.org/pkg/runtime/debug/#SetTraceback. 165 166The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete 167the set of Go environment variables. They influence the building of Go programs 168(see https://golang.org/cmd/go and https://golang.org/pkg/go/build). 169GOARCH, GOOS, and GOROOT are recorded at compile time and made available by 170constants or functions in this package, but they do not influence the execution 171of the run-time system. 172*/ 173package runtime 174 175import "runtime/internal/sys" 176 177// Caller reports file and line number information about function invocations on 178// the calling goroutine's stack. The argument skip is the number of stack frames 179// to ascend, with 0 identifying the caller of Caller. (For historical reasons the 180// meaning of skip differs between Caller and Callers.) The return values report the 181// program counter, file name, and line number within the file of the corresponding 182// call. The boolean ok is false if it was not possible to recover the information. 183func Caller(skip int) (pc uintptr, file string, line int, ok bool) 184 185// Callers fills the slice pc with the return program counters of function invocations 186// on the calling goroutine's stack. The argument skip is the number of stack frames 187// to skip before recording in pc, with 0 identifying the frame for Callers itself and 188// 1 identifying the caller of Callers. 189// It returns the number of entries written to pc. 190// 191// To translate these PCs into symbolic information such as function 192// names and line numbers, use CallersFrames. CallersFrames accounts 193// for inlined functions and adjusts the return program counters into 194// call program counters. Iterating over the returned slice of PCs 195// directly is discouraged, as is using FuncForPC on any of the 196// returned PCs, since these cannot account for inlining or return 197// program counter adjustment. 198func Callers(skip int, pc []uintptr) int 199 200// GOROOT returns the root of the Go tree. It uses the 201// GOROOT environment variable, if set at process start, 202// or else the root used during the Go build. 203func GOROOT() string { 204 s := gogetenv("GOROOT") 205 if s != "" { 206 return s 207 } 208 return sys.DefaultGoroot 209} 210 211// Version returns the Go tree's version string. 212// It is either the commit hash and date at the time of the build or, 213// when possible, a release tag like "go1.3". 214func Version() string { 215 return sys.TheVersion 216} 217 218// GOOS is the running program's operating system target: 219// one of darwin, freebsd, linux, and so on. 220// To view possible combinations of GOOS and GOARCH, run "go tool dist list". 221const GOOS string = sys.GOOS 222 223// GOARCH is the running program's architecture target: 224// one of 386, amd64, arm, s390x, and so on. 225const GOARCH string = sys.GOARCH 226 227// GCCGOTOOLDIR is the Tool Dir for the gccgo build 228const GCCGOTOOLDIR string = sys.GccgoToolDir 229