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Source file src/runtime/extern.go

Documentation: runtime

     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.
     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.
    11  Environment Variables
    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
    39  	never recycled.
    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  	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.
    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.
    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.
    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
    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.
   102  	invalidptr: defaults to invalidptr=1, causing the garbage collector and stack
   103  	copier to crash the program if an invalid pointer value (for example, 1)
   104  	is found in a pointer-typed location. Setting invalidptr=0 disables this check.
   105  	This should only be used as a temporary workaround to diagnose buggy code.
   106  	The real fix is to not store integers in pointer-typed locations.
   108  	sbrk: setting sbrk=1 replaces the memory allocator and garbage collector
   109  	with a trivial allocator that obtains memory from the operating system and
   110  	never reclaims any memory.
   112  	scavenge: scavenge=1 enables debugging mode of heap scavenger.
   114  	scheddetail: setting schedtrace=X and scheddetail=1 causes the scheduler to emit
   115  	detailed multiline info every X milliseconds, describing state of the scheduler,
   116  	processors, threads and goroutines.
   118  	schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard
   119  	error every X milliseconds, summarizing the scheduler state.
   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
   128  the limit.
   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.
   157  */
   158  package runtime
   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.
   172  	var rpc [3]uintptr
   173  	if callers(1+skip-1, rpc[:]) < 2 {
   174  		return
   175  	}
   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)
   182  	if !ok {
   183  		return
   184  	}
   185  	_, frame, _ := stackExpander.next(callers, true)
   186  	pc = frame.PC
   187  	file = frame.File
   188  	line = frame.Line
   189  	return
   190  }
   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.
   197  //
   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.
   209  	if len(pc) == 0 {
   210  		return 0
   211  	}
   212  	return callers(skip, pc)
   213  }
   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")
   220  	if s != "" {
   221  		return s
   222  	}
   223  	return sys.DefaultGoroot
   224  }
   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
   231  }
   233  // GOOS is the running program's operating system target:
   234  // one of darwin, freebsd, linux, and so on.
   235  const GOOS string = sys.GOOS
   237  // GOARCH is the running program's architecture target:
   238  // one of 386, amd64, arm, s390x, and so on.
   239  const GOARCH string = sys.GOARCH

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