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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
    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
    32  	the object.
    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
    43  	never recycled.
    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.
    64  	Currently, it is:
    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
    79  	runtime.GC() call.
    81  	inittrace: setting inittrace=1 causes the runtime to emit a single line to standard
    82  	error for each package with init work, summarizing the execution time and memory
    83  	allocation. No information is printed for inits executed as part of plugin loading
    84  	and for packages without both user defined and compiler generated init work.
    85  	The format of this line is subject to change. Currently, it is:
    86  		init # @#ms, # ms clock, # bytes, # allocs
    87  	where the fields are as follows:
    88  		init #      the package name
    89  		@# ms       time in milliseconds when the init started since program start
    90  		# clock     wall-clock time for package initialization work
    91  		# bytes     memory allocated on the heap
    92  		# allocs    number of heap allocations
    94  	madvdontneed: setting madvdontneed=0 will use MADV_FREE
    95  	instead of MADV_DONTNEED on Linux when returning memory to the
    96  	kernel. This is more efficient, but means RSS numbers will
    97  	drop only when the OS is under memory pressure.
    99  	memprofilerate: setting memprofilerate=X will update the value of runtime.MemProfileRate.
   100  	When set to 0 memory profiling is disabled.  Refer to the description of
   101  	MemProfileRate for the default value.
   103  	invalidptr: invalidptr=1 (the default) causes the garbage collector and stack
   104  	copier to crash the program if an invalid pointer value (for example, 1)
   105  	is found in a pointer-typed location. Setting invalidptr=0 disables this check.
   106  	This should only be used as a temporary workaround to diagnose buggy code.
   107  	The real fix is to not store integers in pointer-typed locations.
   109  	sbrk: setting sbrk=1 replaces the memory allocator and garbage collector
   110  	with a trivial allocator that obtains memory from the operating system and
   111  	never reclaims any memory.
   113  	scavtrace: setting scavtrace=1 causes the runtime to emit a single line to standard
   114  	error, roughly once per GC cycle, summarizing the amount of work done by the
   115  	scavenger as well as the total amount of memory returned to the operating system
   116  	and an estimate of physical memory utilization. The format of this line is subject
   117  	to change, but currently it is:
   118  		scav # # KiB work, # KiB total, #% util
   119  	where the fields are as follows:
   120  		scav #       the scavenge cycle number
   121  		# KiB work   the amount of memory returned to the OS since the last line
   122  		# KiB total  the total amount of memory returned to the OS
   123  		#% util      the fraction of all unscavenged memory which is in-use
   124  	If the line ends with "(forced)", then scavenging was forced by a
   125  	debug.FreeOSMemory() call.
   127  	scheddetail: setting schedtrace=X and scheddetail=1 causes the scheduler to emit
   128  	detailed multiline info every X milliseconds, describing state of the scheduler,
   129  	processors, threads and goroutines.
   131  	schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard
   132  	error every X milliseconds, summarizing the scheduler state.
   134  	tracebackancestors: setting tracebackancestors=N extends tracebacks with the stacks at
   135  	which goroutines were created, where N limits the number of ancestor goroutines to
   136  	report. This also extends the information returned by runtime.Stack. Ancestor's goroutine
   137  	IDs will refer to the ID of the goroutine at the time of creation; it's possible for this
   138  	ID to be reused for another goroutine. Setting N to 0 will report no ancestry information.
   140  	asyncpreemptoff: asyncpreemptoff=1 disables signal-based
   141  	asynchronous goroutine preemption. This makes some loops
   142  	non-preemptible for long periods, which may delay GC and
   143  	goroutine scheduling. This is useful for debugging GC issues
   144  	because it also disables the conservative stack scanning used
   145  	for asynchronously preempted goroutines.
   147  The net, net/http, and crypto/tls packages also refer to debugging variables in GODEBUG.
   148  See the documentation for those packages for details.
   150  The GOMAXPROCS variable limits the number of operating system threads that
   151  can execute user-level Go code simultaneously. There is no limit to the number of threads
   152  that can be blocked in system calls on behalf of Go code; those do not count against
   153  the GOMAXPROCS limit. This package's GOMAXPROCS function queries and changes
   154  the limit.
   156  The GORACE variable configures the race detector, for programs built using -race.
   157  See for details.
   159  The GOTRACEBACK variable controls the amount of output generated when a Go
   160  program fails due to an unrecovered panic or an unexpected runtime condition.
   161  By default, a failure prints a stack trace for the current goroutine,
   162  eliding functions internal to the run-time system, and then exits with exit code 2.
   163  The failure prints stack traces for all goroutines if there is no current goroutine
   164  or the failure is internal to the run-time.
   165  GOTRACEBACK=none omits the goroutine stack traces entirely.
   166  GOTRACEBACK=single (the default) behaves as described above.
   167  GOTRACEBACK=all adds stack traces for all user-created goroutines.
   168  GOTRACEBACK=system is like ``all'' but adds stack frames for run-time functions
   169  and shows goroutines created internally by the run-time.
   170  GOTRACEBACK=crash is like ``system'' but crashes in an operating system-specific
   171  manner instead of exiting. For example, on Unix systems, the crash raises
   172  SIGABRT to trigger a core dump.
   173  For historical reasons, the GOTRACEBACK settings 0, 1, and 2 are synonyms for
   174  none, all, and system, respectively.
   175  The runtime/debug package's SetTraceback function allows increasing the
   176  amount of output at run time, but it cannot reduce the amount below that
   177  specified by the environment variable.
   178  See
   180  The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete
   181  the set of Go environment variables. They influence the building of Go programs
   182  (see and
   183  GOARCH, GOOS, and GOROOT are recorded at compile time and made available by
   184  constants or functions in this package, but they do not influence the execution
   185  of the run-time system.
   186  */
   187  package runtime
   189  import "runtime/internal/sys"
   191  // Caller reports file and line number information about function invocations on
   192  // the calling goroutine's stack. The argument skip is the number of stack frames
   193  // to ascend, with 0 identifying the caller of Caller.  (For historical reasons the
   194  // meaning of skip differs between Caller and Callers.) The return values report the
   195  // program counter, file name, and line number within the file of the corresponding
   196  // call. The boolean ok is false if it was not possible to recover the information.
   197  func Caller(skip int) (pc uintptr, file string, line int, ok bool) {
   198  	rpc := make([]uintptr, 1)
   199  	n := callers(skip+1, rpc[:])
   200  	if n < 1 {
   201  		return
   202  	}
   203  	frame, _ := CallersFrames(rpc).Next()
   204  	return frame.PC, frame.File, frame.Line, frame.PC != 0
   205  }
   207  // Callers fills the slice pc with the return program counters of function invocations
   208  // on the calling goroutine's stack. The argument skip is the number of stack frames
   209  // to skip before recording in pc, with 0 identifying the frame for Callers itself and
   210  // 1 identifying the caller of Callers.
   211  // It returns the number of entries written to pc.
   212  //
   213  // To translate these PCs into symbolic information such as function
   214  // names and line numbers, use CallersFrames. CallersFrames accounts
   215  // for inlined functions and adjusts the return program counters into
   216  // call program counters. Iterating over the returned slice of PCs
   217  // directly is discouraged, as is using FuncForPC on any of the
   218  // returned PCs, since these cannot account for inlining or return
   219  // program counter adjustment.
   220  func Callers(skip int, pc []uintptr) int {
   221  	// runtime.callers uses pc.array==nil as a signal
   222  	// to print a stack trace. Pick off 0-length pc here
   223  	// so that we don't let a nil pc slice get to it.
   224  	if len(pc) == 0 {
   225  		return 0
   226  	}
   227  	return callers(skip, pc)
   228  }
   230  var defaultGOROOT string // set by cmd/link
   232  // GOROOT returns the root of the Go tree. It uses the
   233  // GOROOT environment variable, if set at process start,
   234  // or else the root used during the Go build.
   235  func GOROOT() string {
   236  	s := gogetenv("GOROOT")
   237  	if s != "" {
   238  		return s
   239  	}
   240  	return defaultGOROOT
   241  }
   243  // buildVersion is the Go tree's version string at build time.
   244  //
   245  // If any GOEXPERIMENTs are set to non-default values, it will include
   246  // "X:<GOEXPERIMENT>".
   247  //
   248  // This is set by the linker.
   249  //
   250  // This is accessed by "go version <binary>".
   251  var buildVersion string
   253  // Version returns the Go tree's version string.
   254  // It is either the commit hash and date at the time of the build or,
   255  // when possible, a release tag like "go1.3".
   256  func Version() string {
   257  	return buildVersion
   258  }
   260  // GOOS is the running program's operating system target:
   261  // one of darwin, freebsd, linux, and so on.
   262  // To view possible combinations of GOOS and GOARCH, run "go tool dist list".
   263  const GOOS string = sys.GOOS
   265  // GOARCH is the running program's architecture target:
   266  // one of 386, amd64, arm, s390x, and so on.
   267  const GOARCH string = sys.GOARCH

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