libgo/go/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         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.
  36
  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
  39         never recycled.
  40
  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.
  46
  47         gcpacertrace: setting gcpacertrace=1 causes the garbage collector to
  48         print information about the internal state of the concurrent pacer.
  49
  50         gcshrinkstackoff: setting gcshrinkstackoff=1 disables moving goroutines
  51         onto smaller stacks. In this mode, a goroutine's stack can only grow.
  52
  53         gcrescanstacks: setting gcrescanstacks=1 enables stack
  54         re-scanning during the STW mark termination phase. This is
  55         helpful for debugging if objects are being prematurely
  56         garbage collected.
  57
  58         gcstoptheworld: setting gcstoptheworld=1 disables concurrent garbage collection,
  59         making every garbage collection a stop-the-world event. Setting gcstoptheworld=2
  60         also disables concurrent sweeping after the garbage collection finishes.
  61
  62         gctrace: setting gctrace=1 causes the garbage collector to emit a single line to standard
  63         error at each collection, summarizing the amount of memory collected and the
  64         length of the pause. Setting gctrace=2 emits the same summary but also
  65         repeats each collection. The format of this line is subject to change.
  66         Currently, it is:
  67                 gc # @#s #%: #+#+# ms clock, #+#/#/#+# ms cpu, #->#-># MB, # MB goal, # P
  68         where the fields are as follows:
  69                 gc #        the GC number, incremented at each GC
  70                 @#s         time in seconds since program start
  71                 #%          percentage of time spent in GC since program start
  72                 #+...+#     wall-clock/CPU times for the phases of the GC
  73                 #->#-># MB  heap size at GC start, at GC end, and live heap
  74                 # MB goal   goal heap size
  75                 # P         number of processors used
  76         The phases are stop-the-world (STW) sweep termination, concurrent
  77         mark and scan, and STW mark termination. The CPU times
  78         for mark/scan are broken down in to assist time (GC performed in
  79         line with allocation), background GC time, and idle GC time.
  80         If the line ends with "(forced)", this GC was forced by a
  81         runtime.GC() call.
  82
  83         Setting gctrace to any value > 0 also causes the garbage collector
  84         to emit a summary when memory is released back to the system.
  85         This process of returning memory to the system is called scavenging.
  86         The format of this summary is subject to change.
  87         Currently it is:
  88                 scvg#: # MB released  printed only if non-zero
  89                 scvg#: inuse: # idle: # sys: # released: # consumed: # (MB)
  90         where the fields are as follows:
  91                 scvg#        the scavenge cycle number, incremented at each scavenge
  92                 inuse: #     MB used or partially used spans
  93                 idle: #      MB spans pending scavenging
  94                 sys: #       MB mapped from the system
  95                 released: #  MB released to the system
  96                 consumed: #  MB allocated from the system
  97
  98         memprofilerate: setting memprofilerate=X will update the value of runtime.MemProfileRate.
  99         When set to 0 memory profiling is disabled.  Refer to the description of
 100         MemProfileRate for the default value.
 101
 102         memprofilerate:  setting memprofilerate=X changes the setting for
 103         runtime.MemProfileRate.  Refer to the description of this variable for how
 104         it is used and its default value.
 105
 106         sbrk: setting sbrk=1 replaces the memory allocator and garbage collector
 107         with a trivial allocator that obtains memory from the operating system and
 108         never reclaims any memory.
 109
 110         scavenge: scavenge=1 enables debugging mode of heap scavenger.
 111
 112         scheddetail: setting schedtrace=X and scheddetail=1 causes the scheduler to emit
 113         detailed multiline info every X milliseconds, describing state of the scheduler,
 114         processors, threads and goroutines.
 115
 116         schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard
 117         error every X milliseconds, summarizing the scheduler state.
 118
 119 The net and net/http packages also refer to debugging variables in GODEBUG.
 120 See the documentation for those packages for details.
 121
 122 The GOMAXPROCS variable limits the number of operating system threads that
 123 can execute user-level Go code simultaneously. There is no limit to the number of threads
 124 that can be blocked in system calls on behalf of Go code; those do not count against
 125 the GOMAXPROCS limit. This package's GOMAXPROCS function queries and changes
 126 the limit.
 127
 128 The GOTRACEBACK variable controls the amount of output generated when a Go
 129 program fails due to an unrecovered panic or an unexpected runtime condition.
 130 By default, a failure prints a stack trace for the current goroutine,
 131 eliding functions internal to the run-time system, and then exits with exit code 2.
 132 The failure prints stack traces for all goroutines if there is no current goroutine
 133 or the failure is internal to the run-time.
 134 GOTRACEBACK=none omits the goroutine stack traces entirely.
 135 GOTRACEBACK=single (the default) behaves as described above.
 136 GOTRACEBACK=all adds stack traces for all user-created goroutines.
 137 GOTRACEBACK=system is like ``all'' but adds stack frames for run-time functions
 138 and shows goroutines created internally by the run-time.
 139 GOTRACEBACK=crash is like ``system'' but crashes in an operating system-specific
 140 manner instead of exiting. For example, on Unix systems, the crash raises
 141 SIGABRT to trigger a core dump.
 142 For historical reasons, the GOTRACEBACK settings 0, 1, and 2 are synonyms for
 143 none, all, and system, respectively.
 144 The runtime/debug package's SetTraceback function allows increasing the
 145 amount of output at run time, but it cannot reduce the amount below that
 146 specified by the environment variable.
 147 See https://golang.org/pkg/runtime/debug/#SetTraceback.
 148
 149 The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete
 150 the set of Go environment variables. They influence the building of Go programs
 151 (see https://golang.org/cmd/go and https://golang.org/pkg/go/build).
 152 GOARCH, GOOS, and GOROOT are recorded at compile time and made available by
 153 constants or functions in this package, but they do not influence the execution
 154 of the run-time system.
 155 */
 156 package runtime
 157
 158 import "runtime/internal/sys"
 159
 160 // Caller reports file and line number information about function invocations on
 161 // the calling goroutine's stack. The argument skip is the number of stack frames
 162 // to ascend, with 0 identifying the caller of Caller.  (For historical reasons the
 163 // meaning of skip differs between Caller and Callers.) The return values report the
 164 // program counter, file name, and line number within the file of the corresponding
 165 // call. The boolean ok is false if it was not possible to recover the information.
 166 func Caller(skip int) (pc uintptr, file string, line int, ok bool)
 167
 168 // Callers fills the slice pc with the return program counters of function invocations
 169 // on the calling goroutine's stack. The argument skip is the number of stack frames
 170 // to skip before recording in pc, with 0 identifying the frame for Callers itself and
 171 // 1 identifying the caller of Callers.
 172 // It returns the number of entries written to pc.
 173 //
 174 // To translate these PCs into symbolic information such as function
 175 // names and line numbers, use CallersFrames. CallersFrames accounts
 176 // for inlined functions and adjusts the return program counters into
 177 // call program counters. Iterating over the returned slice of PCs
 178 // directly is discouraged, as is using FuncForPC on any of the
 179 // returned PCs, since these cannot account for inlining or return
 180 // program counter adjustment.
 181 func Callers(skip int, pc []uintptr) int
 182
 183 // GOROOT returns the root of the Go tree. It uses the
 184 // GOROOT environment variable, if set at process start,
 185 // or else the root used during the Go build.
 186 func GOROOT() string {
 187         s := gogetenv("GOROOT")
 188         if s != "" {
 189                 return s
 190         }
 191         return sys.DefaultGoroot
 192 }
 193
 194 // Version returns the Go tree's version string.
 195 // It is either the commit hash and date at the time of the build or,
 196 // when possible, a release tag like "go1.3".
 197 func Version() string {
 198         return sys.TheVersion
 199 }
 200
 201 // GOOS is the running program's operating system target:
 202 // one of darwin, freebsd, linux, and so on.
 203 const GOOS string = sys.GOOS
 204
 205 // GOARCH is the running program's architecture target:
 206 // one of 386, amd64, arm, s390x, and so on.
 207 const GOARCH string = sys.GOARCH
 208
 209 // GCCGOTOOLDIR is the Tool Dir for the gccgo build
 210 const GCCGOTOOLDIR string = sys.GccgoToolDir