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 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
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.
90 invalidptr: invalidptr=1 (the default) causes the garbage collector and stack
91 copier to crash the program if an invalid pointer value (for example, 1)
92 is found in a pointer-typed location. Setting invalidptr=0 disables this check.
93 This should only be used as a temporary workaround to diagnose buggy code.
94 The real fix is to not store integers in pointer-typed locations.
96 sbrk: setting sbrk=1 replaces the memory allocator and garbage collector
97 with a trivial allocator that obtains memory from the operating system and
98 never reclaims any memory.
100 scavenge: scavenge=1 enables debugging mode of heap scavenger.
102 scavtrace: setting scavtrace=1 causes the runtime to emit a single line to standard
103 error, roughly once per GC cycle, summarizing the amount of work done by the
104 scavenger as well as the total amount of memory returned to the operating system
105 and an estimate of physical memory utilization. The format of this line is subject
106 to change, but currently it is:
107 scav # # KiB work, # KiB total, #% util
108 where the fields are as follows:
109 scav # the scavenge cycle number
110 # KiB work the amount of memory returned to the OS since the last line
111 # KiB total the total amount of memory returned to the OS
112 #% util the fraction of all unscavenged memory which is in-use
113 If the line ends with "(forced)", then scavenging was forced by a
114 debug.FreeOSMemory() call.
116 scheddetail: setting schedtrace=X and scheddetail=1 causes the scheduler to emit
117 detailed multiline info every X milliseconds, describing state of the scheduler,
118 processors, threads and goroutines.
120 schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard
121 error every X milliseconds, summarizing the scheduler state.
123 tracebackancestors: setting tracebackancestors=N extends tracebacks with the stacks at
124 which goroutines were created, where N limits the number of ancestor goroutines to
125 report. This also extends the information returned by runtime.Stack. Ancestor's goroutine
126 IDs will refer to the ID of the goroutine at the time of creation; it's possible for this
127 ID to be reused for another goroutine. Setting N to 0 will report no ancestry information.
129 asyncpreemptoff: asyncpreemptoff=1 disables signal-based
130 asynchronous goroutine preemption. This makes some loops
131 non-preemptible for long periods, which may delay GC and
132 goroutine scheduling. This is useful for debugging GC issues
133 because it also disables the conservative stack scanning used
134 for asynchronously preempted goroutines.
136 The net, net/http, and crypto/tls packages also refer to debugging variables in GODEBUG.
137 See the documentation for those packages for details.
139 The GOMAXPROCS variable limits the number of operating system threads that
140 can execute user-level Go code simultaneously. There is no limit to the number of threads
141 that can be blocked in system calls on behalf of Go code; those do not count against
142 the GOMAXPROCS limit. This package's GOMAXPROCS function queries and changes
145 The GORACE variable configures the race detector, for programs built using -race.
146 See https://golang.org/doc/articles/race_detector.html for details.
148 The GOTRACEBACK variable controls the amount of output generated when a Go
149 program fails due to an unrecovered panic or an unexpected runtime condition.
150 By default, a failure prints a stack trace for the current goroutine,
151 eliding functions internal to the run-time system, and then exits with exit code 2.
152 The failure prints stack traces for all goroutines if there is no current goroutine
153 or the failure is internal to the run-time.
154 GOTRACEBACK=none omits the goroutine stack traces entirely.
155 GOTRACEBACK=single (the default) behaves as described above.
156 GOTRACEBACK=all adds stack traces for all user-created goroutines.
157 GOTRACEBACK=system is like ``all'' but adds stack frames for run-time functions
158 and shows goroutines created internally by the run-time.
159 GOTRACEBACK=crash is like ``system'' but crashes in an operating system-specific
160 manner instead of exiting. For example, on Unix systems, the crash raises
161 SIGABRT to trigger a core dump.
162 For historical reasons, the GOTRACEBACK settings 0, 1, and 2 are synonyms for
163 none, all, and system, respectively.
164 The runtime/debug package's SetTraceback function allows increasing the
165 amount of output at run time, but it cannot reduce the amount below that
166 specified by the environment variable.
167 See https://golang.org/pkg/runtime/debug/#SetTraceback.
169 The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete
170 the set of Go environment variables. They influence the building of Go programs
171 (see https://golang.org/cmd/go and https://golang.org/pkg/go/build).
172 GOARCH, GOOS, and GOROOT are recorded at compile time and made available by
173 constants or functions in this package, but they do not influence the execution
174 of the run-time system.
178 import "runtime/internal/sys"
180 // Caller reports file and line number information about function invocations on
181 // the calling goroutine's stack. The argument skip is the number of stack frames
182 // to ascend, with 0 identifying the caller of Caller. (For historical reasons the
183 // meaning of skip differs between Caller and Callers.) The return values report the
184 // program counter, file name, and line number within the file of the corresponding
185 // call. The boolean ok is false if it was not possible to recover the information.
186 func Caller(skip int) (pc uintptr, file string, line int, ok bool) {
187 rpc := make([]uintptr, 1)
188 n := callers(skip+1, rpc[:])
192 frame, _ := CallersFrames(rpc).Next()
193 return frame.PC, frame.File, frame.Line, frame.PC != 0
196 // Callers fills the slice pc with the return program counters of function invocations
197 // on the calling goroutine's stack. The argument skip is the number of stack frames
198 // to skip before recording in pc, with 0 identifying the frame for Callers itself and
199 // 1 identifying the caller of Callers.
200 // It returns the number of entries written to pc.
202 // To translate these PCs into symbolic information such as function
203 // names and line numbers, use CallersFrames. CallersFrames accounts
204 // for inlined functions and adjusts the return program counters into
205 // call program counters. Iterating over the returned slice of PCs
206 // directly is discouraged, as is using FuncForPC on any of the
207 // returned PCs, since these cannot account for inlining or return
208 // program counter adjustment.
209 func Callers(skip int, pc []uintptr) int {
210 // runtime.callers uses pc.array==nil as a signal
211 // to print a stack trace. Pick off 0-length pc here
212 // so that we don't let a nil pc slice get to it.
216 return callers(skip, pc)
219 // GOROOT returns the root of the Go tree. It uses the
220 // GOROOT environment variable, if set at process start,
221 // or else the root used during the Go build.
222 func GOROOT() string {
223 s := gogetenv("GOROOT")
227 return sys.DefaultGoroot
230 // Version returns the Go tree's version string.
231 // It is either the commit hash and date at the time of the build or,
232 // when possible, a release tag like "go1.3".
233 func Version() string {
234 return sys.TheVersion
237 // GOOS is the running program's operating system target:
238 // one of darwin, freebsd, linux, and so on.
239 // To view possible combinations of GOOS and GOARCH, run "go tool dist list".
240 const GOOS string = sys.GOOS
242 // GOARCH is the running program's architecture target:
243 // one of 386, amd64, arm, s390x, and so on.
244 const GOARCH string = sys.GOARCH