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 cgocheck: setting cgocheck=0 disables all checks for packages
31 using cgo to incorrectly pass Go pointers to non-Go code.
32 Setting cgocheck=1 (the default) enables relatively cheap
33 checks that may miss some errors. Setting cgocheck=2 enables
34 expensive checks that should not miss any errors, but will
35 cause your program to run slower.
37 efence: setting efence=1 causes the allocator to run in a mode
38 where each object is allocated on a unique page and addresses are
41 gccheckmark: setting gccheckmark=1 enables verification of the
42 garbage collector's concurrent mark phase by performing a
43 second mark pass while the world is stopped. If the second
44 pass finds a reachable object that was not found by concurrent
45 mark, the garbage collector will panic.
47 gcpacertrace: setting gcpacertrace=1 causes the garbage collector to
48 print information about the internal state of the concurrent pacer.
50 gcshrinkstackoff: setting gcshrinkstackoff=1 disables moving goroutines
51 onto smaller stacks. In this mode, a goroutine's stack can only grow.
53 gcstoptheworld: setting gcstoptheworld=1 disables concurrent garbage collection,
54 making every garbage collection a stop-the-world event. Setting gcstoptheworld=2
55 also disables concurrent sweeping after the garbage collection finishes.
57 gctrace: setting gctrace=1 causes the garbage collector to emit a single line to standard
58 error at each collection, summarizing the amount of memory collected and the
59 length of the pause. The format of this line is subject to change.
61 gc # @#s #%: #+#+# ms clock, #+#/#/#+# ms cpu, #->#-># MB, # MB goal, # P
62 where the fields are as follows:
63 gc # the GC number, incremented at each GC
64 @#s time in seconds since program start
65 #% percentage of time spent in GC since program start
66 #+...+# wall-clock/CPU times for the phases of the GC
67 #->#-># MB heap size at GC start, at GC end, and live heap
68 # MB goal goal heap size
69 # P number of processors used
70 The phases are stop-the-world (STW) sweep termination, concurrent
71 mark and scan, and STW mark termination. The CPU times
72 for mark/scan are broken down in to assist time (GC performed in
73 line with allocation), background GC time, and idle GC time.
74 If the line ends with "(forced)", this GC was forced by a
77 Setting gctrace to any value > 0 also causes the garbage collector
78 to emit a summary when memory is released back to the system.
79 This process of returning memory to the system is called scavenging.
80 The format of this summary is subject to change.
82 scvg#: # MB released printed only if non-zero
83 scvg#: inuse: # idle: # sys: # released: # consumed: # (MB)
84 where the fields are as follows:
85 scvg# the scavenge cycle number, incremented at each scavenge
86 inuse: # MB used or partially used spans
87 idle: # MB spans pending scavenging
88 sys: # MB mapped from the system
89 released: # MB released to the system
90 consumed: # MB allocated from the system
92 memprofilerate: setting memprofilerate=X will update the value of runtime.MemProfileRate.
93 When set to 0 memory profiling is disabled. Refer to the description of
94 MemProfileRate for the default value.
96 invalidptr: defaults to invalidptr=1, causing the garbage collector and stack
97 copier to crash the program if an invalid pointer value (for example, 1)
98 is found in a pointer-typed location. Setting invalidptr=0 disables this check.
99 This should only be used as a temporary workaround to diagnose buggy code.
100 The real fix is to not store integers in pointer-typed locations.
102 sbrk: setting sbrk=1 replaces the memory allocator and garbage collector
103 with a trivial allocator that obtains memory from the operating system and
104 never reclaims any memory.
106 scavenge: scavenge=1 enables debugging mode of heap scavenger.
108 scheddetail: setting schedtrace=X and scheddetail=1 causes the scheduler to emit
109 detailed multiline info every X milliseconds, describing state of the scheduler,
110 processors, threads and goroutines.
112 schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard
113 error every X milliseconds, summarizing the scheduler state.
115 tracebackancestors: setting tracebackancestors=N extends tracebacks with the stacks at
116 which goroutines were created, where N limits the number of ancestor goroutines to
117 report. This also extends the information returned by runtime.Stack. Ancestor's goroutine
118 IDs will refer to the ID of the goroutine at the time of creation; it's possible for this
119 ID to be reused for another goroutine. Setting N to 0 will report no ancestry information.
121 The net and net/http packages also refer to debugging variables in GODEBUG.
122 See the documentation for those packages for details.
124 The GOMAXPROCS variable limits the number of operating system threads that
125 can execute user-level Go code simultaneously. There is no limit to the number of threads
126 that can be blocked in system calls on behalf of Go code; those do not count against
127 the GOMAXPROCS limit. This package's GOMAXPROCS function queries and changes
130 The GOTRACEBACK variable controls the amount of output generated when a Go
131 program fails due to an unrecovered panic or an unexpected runtime condition.
132 By default, a failure prints a stack trace for the current goroutine,
133 eliding functions internal to the run-time system, and then exits with exit code 2.
134 The failure prints stack traces for all goroutines if there is no current goroutine
135 or the failure is internal to the run-time.
136 GOTRACEBACK=none omits the goroutine stack traces entirely.
137 GOTRACEBACK=single (the default) behaves as described above.
138 GOTRACEBACK=all adds stack traces for all user-created goroutines.
139 GOTRACEBACK=system is like ``all'' but adds stack frames for run-time functions
140 and shows goroutines created internally by the run-time.
141 GOTRACEBACK=crash is like ``system'' but crashes in an operating system-specific
142 manner instead of exiting. For example, on Unix systems, the crash raises
143 SIGABRT to trigger a core dump.
144 For historical reasons, the GOTRACEBACK settings 0, 1, and 2 are synonyms for
145 none, all, and system, respectively.
146 The runtime/debug package's SetTraceback function allows increasing the
147 amount of output at run time, but it cannot reduce the amount below that
148 specified by the environment variable.
149 See https://golang.org/pkg/runtime/debug/#SetTraceback.
151 The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete
152 the set of Go environment variables. They influence the building of Go programs
153 (see https://golang.org/cmd/go and https://golang.org/pkg/go/build).
154 GOARCH, GOOS, and GOROOT are recorded at compile time and made available by
155 constants or functions in this package, but they do not influence the execution
156 of the run-time system.
160 import "runtime/internal/sys"
162 // Caller reports file and line number information about function invocations on
163 // the calling goroutine's stack. The argument skip is the number of stack frames
164 // to ascend, with 0 identifying the caller of Caller. (For historical reasons the
165 // meaning of skip differs between Caller and Callers.) The return values report the
166 // program counter, file name, and line number within the file of the corresponding
167 // call. The boolean ok is false if it was not possible to recover the information.
168 func Caller(skip int) (pc uintptr, file string, line int, ok bool) {
169 // Make room for three PCs: the one we were asked for,
170 // what it called, so that CallersFrames can see if it "called"
171 // sigpanic, and possibly a PC for skipPleaseUseCallersFrames.
173 if callers(skip, rpc[:]) < 2 {
176 var stackExpander stackExpander
177 callers := stackExpander.init(rpc[:])
178 // We asked for one extra, so skip that one. If this is sigpanic,
179 // stepping over this frame will set up state in Frames so the
180 // next frame is correct.
181 callers, _, ok = stackExpander.next(callers, true)
185 _, frame, _ := stackExpander.next(callers, true)
192 // Callers fills the slice pc with the return program counters of function invocations
193 // on the calling goroutine's stack. The argument skip is the number of stack frames
194 // to skip before recording in pc, with 0 identifying the frame for Callers itself and
195 // 1 identifying the caller of Callers.
196 // It returns the number of entries written to pc.
198 // To translate these PCs into symbolic information such as function
199 // names and line numbers, use CallersFrames. CallersFrames accounts
200 // for inlined functions and adjusts the return program counters into
201 // call program counters. Iterating over the returned slice of PCs
202 // directly is discouraged, as is using FuncForPC on any of the
203 // returned PCs, since these cannot account for inlining or return
204 // program counter adjustment.
205 func Callers(skip int, pc []uintptr) int {
206 // runtime.callers uses pc.array==nil as a signal
207 // to print a stack trace. Pick off 0-length pc here
208 // so that we don't let a nil pc slice get to it.
212 return callers(skip, pc)
215 // GOROOT returns the root of the Go tree. It uses the
216 // GOROOT environment variable, if set at process start,
217 // or else the root used during the Go build.
218 func GOROOT() string {
219 s := gogetenv("GOROOT")
223 return sys.DefaultGoroot
226 // Version returns the Go tree's version string.
227 // It is either the commit hash and date at the time of the build or,
228 // when possible, a release tag like "go1.3".
229 func Version() string {
230 return sys.TheVersion
233 // GOOS is the running program's operating system target:
234 // one of darwin, freebsd, linux, and so on.
235 // To view possible combinations of GOOS and GOARCH, run "go tool dist list".
236 const GOOS string = sys.GOOS
238 // GOARCH is the running program's architecture target:
239 // one of 386, amd64, arm, s390x, and so on.
240 const GOARCH string = sys.GOARCH