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         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.
  56
  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.
  60         Currently, it is:
  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
  75         runtime.GC() call.
  76
  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.
  81         Currently it is:
  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
  91
  92         madvdontneed: setting madvdontneed=1 will use MADV_DONTNEED
  93         instead of MADV_FREE on Linux when returning memory to the
  94         kernel. This is less efficient, but causes RSS numbers to drop
  95         more quickly.
  96
  97         memprofilerate: setting memprofilerate=X will update the value of runtime.MemProfileRate.
  98         When set to 0 memory profiling is disabled.  Refer to the description of
  99         MemProfileRate for the default value.
 100
 101         memprofilerate:  setting memprofilerate=X changes the setting for
 102         runtime.MemProfileRate.  Refer to the description of this variable for how
 103         it is used and its default value.
 104
 105         sbrk: setting sbrk=1 replaces the memory allocator and garbage collector
 106         with a trivial allocator that obtains memory from the operating system and
 107         never reclaims any memory.
 108
 109         scavenge: scavenge=1 enables debugging mode of heap scavenger.
 110
 111         scheddetail: setting schedtrace=X and scheddetail=1 causes the scheduler to emit
 112         detailed multiline info every X milliseconds, describing state of the scheduler,
 113         processors, threads and goroutines.
 114
 115         schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard
 116         error every X milliseconds, summarizing the scheduler state.
 117
 118         tracebackancestors: setting tracebackancestors=N extends tracebacks with the stacks at
 119         which goroutines were created, where N limits the number of ancestor goroutines to
 120         report. This also extends the information returned by runtime.Stack. Ancestor's goroutine
 121         IDs will refer to the ID of the goroutine at the time of creation; it's possible for this
 122         ID to be reused for another goroutine. Setting N to 0 will report no ancestry information.
 123
 124 The net and net/http packages also refer to debugging variables in GODEBUG.
 125 See the documentation for those packages for details.
 126
 127 The GOMAXPROCS variable limits the number of operating system threads that
 128 can execute user-level Go code simultaneously. There is no limit to the number of threads
 129 that can be blocked in system calls on behalf of Go code; those do not count against
 130 the GOMAXPROCS limit. This package's GOMAXPROCS function queries and changes
 131 the limit.
 132
 133 The GOTRACEBACK variable controls the amount of output generated when a Go
 134 program fails due to an unrecovered panic or an unexpected runtime condition.
 135 By default, a failure prints a stack trace for the current goroutine,
 136 eliding functions internal to the run-time system, and then exits with exit code 2.
 137 The failure prints stack traces for all goroutines if there is no current goroutine
 138 or the failure is internal to the run-time.
 139 GOTRACEBACK=none omits the goroutine stack traces entirely.
 140 GOTRACEBACK=single (the default) behaves as described above.
 141 GOTRACEBACK=all adds stack traces for all user-created goroutines.
 142 GOTRACEBACK=system is like ``all'' but adds stack frames for run-time functions
 143 and shows goroutines created internally by the run-time.
 144 GOTRACEBACK=crash is like ``system'' but crashes in an operating system-specific
 145 manner instead of exiting. For example, on Unix systems, the crash raises
 146 SIGABRT to trigger a core dump.
 147 For historical reasons, the GOTRACEBACK settings 0, 1, and 2 are synonyms for
 148 none, all, and system, respectively.
 149 The runtime/debug package's SetTraceback function allows increasing the
 150 amount of output at run time, but it cannot reduce the amount below that
 151 specified by the environment variable.
 152 See https://golang.org/pkg/runtime/debug/#SetTraceback.
 153
 154 The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete
 155 the set of Go environment variables. They influence the building of Go programs
 156 (see https://golang.org/cmd/go and https://golang.org/pkg/go/build).
 157 GOARCH, GOOS, and GOROOT are recorded at compile time and made available by
 158 constants or functions in this package, but they do not influence the execution
 159 of the run-time system.
 160 */
 161 package runtime
 162
 163 import "runtime/internal/sys"
 164
 165 // Caller reports file and line number information about function invocations on
 166 // the calling goroutine's stack. The argument skip is the number of stack frames
 167 // to ascend, with 0 identifying the caller of Caller.  (For historical reasons the
 168 // meaning of skip differs between Caller and Callers.) The return values report the
 169 // program counter, file name, and line number within the file of the corresponding
 170 // call. The boolean ok is false if it was not possible to recover the information.
 171 func Caller(skip int) (pc uintptr, file string, line int, ok bool)
 172
 173 // Callers fills the slice pc with the return program counters of function invocations
 174 // on the calling goroutine's stack. The argument skip is the number of stack frames
 175 // to skip before recording in pc, with 0 identifying the frame for Callers itself and
 176 // 1 identifying the caller of Callers.
 177 // It returns the number of entries written to pc.
 178 //
 179 // To translate these PCs into symbolic information such as function
 180 // names and line numbers, use CallersFrames. CallersFrames accounts
 181 // for inlined functions and adjusts the return program counters into
 182 // call program counters. Iterating over the returned slice of PCs
 183 // directly is discouraged, as is using FuncForPC on any of the
 184 // returned PCs, since these cannot account for inlining or return
 185 // program counter adjustment.
 186 func Callers(skip int, pc []uintptr) int
 187
 188 // GOROOT returns the root of the Go tree. It uses the
 189 // GOROOT environment variable, if set at process start,
 190 // or else the root used during the Go build.
 191 func GOROOT() string {
 192         s := gogetenv("GOROOT")
 193         if s != "" {
 194                 return s
 195         }
 196         return sys.DefaultGoroot
 197 }
 198
 199 // Version returns the Go tree's version string.
 200 // It is either the commit hash and date at the time of the build or,
 201 // when possible, a release tag like "go1.3".
 202 func Version() string {
 203         return sys.TheVersion
 204 }
 205
 206 // GOOS is the running program's operating system target:
 207 // one of darwin, freebsd, linux, and so on.
 208 // To view possible combinations of GOOS and GOARCH, run "go tool dist list".
 209 const GOOS string = sys.GOOS
 210
 211 // GOARCH is the running program's architecture target:
 212 // one of 386, amd64, arm, s390x, and so on.
 213 const GOARCH string = sys.GOARCH
 214
 215 // GCCGOTOOLDIR is the Tool Dir for the gccgo build
 216 const GCCGOTOOLDIR string = sys.GccgoToolDir