Source file src/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.
     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  [runtime/debug.SetGCPercent] allows changing this percentage at run time.
    23  The GOMEMLIMIT variable sets a soft memory limit for the runtime. This memory limit
    24  includes the Go heap and all other memory managed by the runtime, and excludes
    25  external memory sources such as mappings of the binary itself, memory managed in
    26  other languages, and memory held by the operating system on behalf of the Go
    27  program. GOMEMLIMIT is a numeric value in bytes with an optional unit suffix.
    28  The supported suffixes include B, KiB, MiB, GiB, and TiB. These suffixes
    29  represent quantities of bytes as defined by the IEC 80000-13 standard. That is,
    30  they are based on powers of two: KiB means 2^10 bytes, MiB means 2^20 bytes,
    31  and so on. The default setting is math.MaxInt64, which effectively disables the
    32  memory limit. [runtime/debug.SetMemoryLimit] allows changing this limit at run
    33  time.
    35  The GODEBUG variable controls debugging variables within the runtime.
    36  It is a comma-separated list of name=val pairs setting these named variables:
    38  	allocfreetrace: setting allocfreetrace=1 causes every allocation to be
    39  	profiled and a stack trace printed on each object's allocation and free.
    41  	clobberfree: setting clobberfree=1 causes the garbage collector to
    42  	clobber the memory content of an object with bad content when it frees
    43  	the object.
    45  	cpu.*: cpu.all=off disables the use of all optional instruction set extensions.
    46  	cpu.extension=off disables use of instructions from the specified instruction set extension.
    47  	extension is the lower case name for the instruction set extension such as sse41 or avx
    48  	as listed in internal/cpu package. As an example cpu.avx=off disables runtime detection
    49  	and thereby use of AVX instructions.
    51  	cgocheck: setting cgocheck=0 disables all checks for packages
    52  	using cgo to incorrectly pass Go pointers to non-Go code.
    53  	Setting cgocheck=1 (the default) enables relatively cheap
    54  	checks that may miss some errors.  Setting cgocheck=2 enables
    55  	expensive checks that should not miss any errors, but will
    56  	cause your program to run slower.
    58  	efence: setting efence=1 causes the allocator to run in a mode
    59  	where each object is allocated on a unique page and addresses are
    60  	never recycled.
    62  	gccheckmark: setting gccheckmark=1 enables verification of the
    63  	garbage collector's concurrent mark phase by performing a
    64  	second mark pass while the world is stopped.  If the second
    65  	pass finds a reachable object that was not found by concurrent
    66  	mark, the garbage collector will panic.
    68  	gcpacertrace: setting gcpacertrace=1 causes the garbage collector to
    69  	print information about the internal state of the concurrent pacer.
    71  	gcshrinkstackoff: setting gcshrinkstackoff=1 disables moving goroutines
    72  	onto smaller stacks. In this mode, a goroutine's stack can only grow.
    74  	gcstoptheworld: setting gcstoptheworld=1 disables concurrent garbage collection,
    75  	making every garbage collection a stop-the-world event. Setting gcstoptheworld=2
    76  	also disables concurrent sweeping after the garbage collection finishes.
    78  	gctrace: setting gctrace=1 causes the garbage collector to emit a single line to standard
    79  	error at each collection, summarizing the amount of memory collected and the
    80  	length of the pause. The format of this line is subject to change.
    81  	Currently, it is:
    82  		gc # @#s #%: #+#+# ms clock, #+#/#/#+# ms cpu, #->#-># MB, # MB goal, # MB stacks, #MB globals, # P
    83  	where the fields are as follows:
    84  		gc #         the GC number, incremented at each GC
    85  		@#s          time in seconds since program start
    86  		#%           percentage of time spent in GC since program start
    87  		#+...+#      wall-clock/CPU times for the phases of the GC
    88  		#->#-># MB   heap size at GC start, at GC end, and live heap
    89  		# MB goal    goal heap size
    90  		# MB stacks  estimated scannable stack size
    91  		# MB globals scannable global size
    92  		# P          number of processors used
    93  	The phases are stop-the-world (STW) sweep termination, concurrent
    94  	mark and scan, and STW mark termination. The CPU times
    95  	for mark/scan are broken down in to assist time (GC performed in
    96  	line with allocation), background GC time, and idle GC time.
    97  	If the line ends with "(forced)", this GC was forced by a
    98  	runtime.GC() call.
   100  	harddecommit: setting harddecommit=1 causes memory that is returned to the OS to
   101  	also have protections removed on it. This is the only mode of operation on Windows,
   102  	but is helpful in debugging scavenger-related issues on other platforms. Currently,
   103  	only supported on Linux.
   105  	inittrace: setting inittrace=1 causes the runtime to emit a single line to standard
   106  	error for each package with init work, summarizing the execution time and memory
   107  	allocation. No information is printed for inits executed as part of plugin loading
   108  	and for packages without both user defined and compiler generated init work.
   109  	The format of this line is subject to change. Currently, it is:
   110  		init # @#ms, # ms clock, # bytes, # allocs
   111  	where the fields are as follows:
   112  		init #      the package name
   113  		@# ms       time in milliseconds when the init started since program start
   114  		# clock     wall-clock time for package initialization work
   115  		# bytes     memory allocated on the heap
   116  		# allocs    number of heap allocations
   118  	madvdontneed: setting madvdontneed=0 will use MADV_FREE
   119  	instead of MADV_DONTNEED on Linux when returning memory to the
   120  	kernel. This is more efficient, but means RSS numbers will
   121  	drop only when the OS is under memory pressure. On the BSDs and
   122  	Illumos/Solaris, setting madvdontneed=1 will use MADV_DONTNEED instead
   123  	of MADV_FREE. This is less efficient, but causes RSS numbers to drop
   124  	more quickly.
   126  	memprofilerate: setting memprofilerate=X will update the value of runtime.MemProfileRate.
   127  	When set to 0 memory profiling is disabled.  Refer to the description of
   128  	MemProfileRate for the default value.
   130  	pagetrace: setting pagetrace=/path/to/file will write out a trace of page events
   131  	that can be viewed, analyzed, and visualized using the x/debug/cmd/pagetrace tool.
   132  	Build your program with GOEXPERIMENT=pagetrace to enable this functionality. Do not
   133  	enable this functionality if your program is a setuid binary as it introduces a security
   134  	risk in that scenario. Currently not supported on Windows, plan9 or js/wasm. Setting this
   135  	option for some applications can produce large traces, so use with care.
   137  	invalidptr: invalidptr=1 (the default) causes the garbage collector and stack
   138  	copier to crash the program if an invalid pointer value (for example, 1)
   139  	is found in a pointer-typed location. Setting invalidptr=0 disables this check.
   140  	This should only be used as a temporary workaround to diagnose buggy code.
   141  	The real fix is to not store integers in pointer-typed locations.
   143  	sbrk: setting sbrk=1 replaces the memory allocator and garbage collector
   144  	with a trivial allocator that obtains memory from the operating system and
   145  	never reclaims any memory.
   147  	scavtrace: setting scavtrace=1 causes the runtime to emit a single line to standard
   148  	error, roughly once per GC cycle, summarizing the amount of work done by the
   149  	scavenger as well as the total amount of memory returned to the operating system
   150  	and an estimate of physical memory utilization. The format of this line is subject
   151  	to change, but currently it is:
   152  		scav # KiB work, # KiB total, #% util
   153  	where the fields are as follows:
   154  		# KiB work   the amount of memory returned to the OS since the last line
   155  		# KiB total  the total amount of memory returned to the OS
   156  		#% util      the fraction of all unscavenged memory which is in-use
   157  	If the line ends with "(forced)", then scavenging was forced by a
   158  	debug.FreeOSMemory() call.
   160  	scheddetail: setting schedtrace=X and scheddetail=1 causes the scheduler to emit
   161  	detailed multiline info every X milliseconds, describing state of the scheduler,
   162  	processors, threads and goroutines.
   164  	schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard
   165  	error every X milliseconds, summarizing the scheduler state.
   167  	tracebackancestors: setting tracebackancestors=N extends tracebacks with the stacks at
   168  	which goroutines were created, where N limits the number of ancestor goroutines to
   169  	report. This also extends the information returned by runtime.Stack. Ancestor's goroutine
   170  	IDs will refer to the ID of the goroutine at the time of creation; it's possible for this
   171  	ID to be reused for another goroutine. Setting N to 0 will report no ancestry information.
   173  	asyncpreemptoff: asyncpreemptoff=1 disables signal-based
   174  	asynchronous goroutine preemption. This makes some loops
   175  	non-preemptible for long periods, which may delay GC and
   176  	goroutine scheduling. This is useful for debugging GC issues
   177  	because it also disables the conservative stack scanning used
   178  	for asynchronously preempted goroutines.
   180  The net and net/http packages also refer to debugging variables in GODEBUG.
   181  See the documentation for those packages for details.
   183  The GOMAXPROCS variable limits the number of operating system threads that
   184  can execute user-level Go code simultaneously. There is no limit to the number of threads
   185  that can be blocked in system calls on behalf of Go code; those do not count against
   186  the GOMAXPROCS limit. This package's GOMAXPROCS function queries and changes
   187  the limit.
   189  The GORACE variable configures the race detector, for programs built using -race.
   190  See for details.
   192  The GOTRACEBACK variable controls the amount of output generated when a Go
   193  program fails due to an unrecovered panic or an unexpected runtime condition.
   194  By default, a failure prints a stack trace for the current goroutine,
   195  eliding functions internal to the run-time system, and then exits with exit code 2.
   196  The failure prints stack traces for all goroutines if there is no current goroutine
   197  or the failure is internal to the run-time.
   198  GOTRACEBACK=none omits the goroutine stack traces entirely.
   199  GOTRACEBACK=single (the default) behaves as described above.
   200  GOTRACEBACK=all adds stack traces for all user-created goroutines.
   201  GOTRACEBACK=system is like “all” but adds stack frames for run-time functions
   202  and shows goroutines created internally by the run-time.
   203  GOTRACEBACK=crash is like “system” but crashes in an operating system-specific
   204  manner instead of exiting. For example, on Unix systems, the crash raises
   205  SIGABRT to trigger a core dump.
   206  For historical reasons, the GOTRACEBACK settings 0, 1, and 2 are synonyms for
   207  none, all, and system, respectively.
   208  The runtime/debug package's SetTraceback function allows increasing the
   209  amount of output at run time, but it cannot reduce the amount below that
   210  specified by the environment variable.
   211  See
   213  The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete
   214  the set of Go environment variables. They influence the building of Go programs
   215  (see and
   216  GOARCH, GOOS, and GOROOT are recorded at compile time and made available by
   217  constants or functions in this package, but they do not influence the execution
   218  of the run-time system.
   219  */
   220  package runtime
   222  import (
   223  	"internal/goarch"
   224  	"internal/goos"
   225  )
   227  // Caller reports file and line number information about function invocations on
   228  // the calling goroutine's stack. The argument skip is the number of stack frames
   229  // to ascend, with 0 identifying the caller of Caller.  (For historical reasons the
   230  // meaning of skip differs between Caller and Callers.) The return values report the
   231  // program counter, file name, and line number within the file of the corresponding
   232  // call. The boolean ok is false if it was not possible to recover the information.
   233  func Caller(skip int) (pc uintptr, file string, line int, ok bool) {
   234  	rpc := make([]uintptr, 1)
   235  	n := callers(skip+1, rpc[:])
   236  	if n < 1 {
   237  		return
   238  	}
   239  	frame, _ := CallersFrames(rpc).Next()
   240  	return frame.PC, frame.File, frame.Line, frame.PC != 0
   241  }
   243  // Callers fills the slice pc with the return program counters of function invocations
   244  // on the calling goroutine's stack. The argument skip is the number of stack frames
   245  // to skip before recording in pc, with 0 identifying the frame for Callers itself and
   246  // 1 identifying the caller of Callers.
   247  // It returns the number of entries written to pc.
   248  //
   249  // To translate these PCs into symbolic information such as function
   250  // names and line numbers, use CallersFrames. CallersFrames accounts
   251  // for inlined functions and adjusts the return program counters into
   252  // call program counters. Iterating over the returned slice of PCs
   253  // directly is discouraged, as is using FuncForPC on any of the
   254  // returned PCs, since these cannot account for inlining or return
   255  // program counter adjustment.
   256  func Callers(skip int, pc []uintptr) int {
   257  	// runtime.callers uses pc.array==nil as a signal
   258  	// to print a stack trace. Pick off 0-length pc here
   259  	// so that we don't let a nil pc slice get to it.
   260  	if len(pc) == 0 {
   261  		return 0
   262  	}
   263  	return callers(skip, pc)
   264  }
   266  var defaultGOROOT string // set by cmd/link
   268  // GOROOT returns the root of the Go tree. It uses the
   269  // GOROOT environment variable, if set at process start,
   270  // or else the root used during the Go build.
   271  func GOROOT() string {
   272  	s := gogetenv("GOROOT")
   273  	if s != "" {
   274  		return s
   275  	}
   276  	return defaultGOROOT
   277  }
   279  // buildVersion is the Go tree's version string at build time.
   280  //
   281  // If any GOEXPERIMENTs are set to non-default values, it will include
   282  // "X:<GOEXPERIMENT>".
   283  //
   284  // This is set by the linker.
   285  //
   286  // This is accessed by "go version <binary>".
   287  var buildVersion string
   289  // Version returns the Go tree's version string.
   290  // It is either the commit hash and date at the time of the build or,
   291  // when possible, a release tag like "go1.3".
   292  func Version() string {
   293  	return buildVersion
   294  }
   296  // GOOS is the running program's operating system target:
   297  // one of darwin, freebsd, linux, and so on.
   298  // To view possible combinations of GOOS and GOARCH, run "go tool dist list".
   299  const GOOS string = goos.GOOS
   301  // GOARCH is the running program's architecture target:
   302  // one of 386, amd64, arm, s390x, and so on.
   303  const GOARCH string = goarch.GOARCH

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