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.
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.
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.
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.
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:
27 allocfreetrace: setting allocfreetrace=1 causes every allocation to be
28 profiled and a stack trace printed on each object's allocation and free.
30 clobberfree: setting clobberfree=1 causes the garbage collector to
31 clobber the memory content of an object with bad content when it frees
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.
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
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.
51 gcpacertrace: setting gcpacertrace=1 causes the garbage collector to
52 print information about the internal state of the concurrent pacer.
54 gcshrinkstackoff: setting gcshrinkstackoff=1 disables moving goroutines
55 onto smaller stacks. In this mode, a goroutine's stack can only grow.
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.
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.
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
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.
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
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.
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.
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.
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.
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.
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.
136 schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard
137 error every X milliseconds, summarizing the scheduler state.
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.
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.
152 The net and net/http packages also refer to debugging variables in GODEBUG.
153 See the documentation for those packages for details.
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
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.
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.
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.
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[:])
211 frame, _ := CallersFrames(rpc).Next()
212 return frame.PC, frame.File, frame.Line, frame.PC != 0
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.
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.
235 return callers(skip, pc)
238 var defaultGOROOT string // set by cmd/link
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")
251 // buildVersion is the Go tree's version string at build time.
253 // If any GOEXPERIMENTs are set to non-default values, it will include
254 // "X:<GOEXPERIMENT>".
256 // This is set by the linker.
258 // This is accessed by "go version <binary>".
259 var buildVersion string
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 {
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
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