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.
     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  [runtime/debug.SetGCPercent] allows changing this percentage at run time.
    22  
    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.
    34  
    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:
    37  
    38  	allocfreetrace: setting allocfreetrace=1 causes every allocation to be
    39  	profiled and a stack trace printed on each object's allocation and free.
    40  
    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.
    44  
    45  	cgocheck: setting cgocheck=0 disables all checks for packages
    46  	using cgo to incorrectly pass Go pointers to non-Go code.
    47  	Setting cgocheck=1 (the default) enables relatively cheap
    48  	checks that may miss some errors.  Setting cgocheck=2 enables
    49  	expensive checks that should not miss any errors, but will
    50  	cause your program to run slower.
    51  
    52  	efence: setting efence=1 causes the allocator to run in a mode
    53  	where each object is allocated on a unique page and addresses are
    54  	never recycled.
    55  
    56  	gccheckmark: setting gccheckmark=1 enables verification of the
    57  	garbage collector's concurrent mark phase by performing a
    58  	second mark pass while the world is stopped.  If the second
    59  	pass finds a reachable object that was not found by concurrent
    60  	mark, the garbage collector will panic.
    61  
    62  	gcpacertrace: setting gcpacertrace=1 causes the garbage collector to
    63  	print information about the internal state of the concurrent pacer.
    64  
    65  	gcshrinkstackoff: setting gcshrinkstackoff=1 disables moving goroutines
    66  	onto smaller stacks. In this mode, a goroutine's stack can only grow.
    67  
    68  	gcstoptheworld: setting gcstoptheworld=1 disables concurrent garbage collection,
    69  	making every garbage collection a stop-the-world event. Setting gcstoptheworld=2
    70  	also disables concurrent sweeping after the garbage collection finishes.
    71  
    72  	gctrace: setting gctrace=1 causes the garbage collector to emit a single line to standard
    73  	error at each collection, summarizing the amount of memory collected and the
    74  	length of the pause. The format of this line is subject to change.
    75  	Currently, it is:
    76  		gc # @#s #%: #+#+# ms clock, #+#/#/#+# ms cpu, #->#-># MB, # MB goal, # P
    77  	where the fields are as follows:
    78  		gc #         the GC number, incremented at each GC
    79  		@#s          time in seconds since program start
    80  		#%           percentage of time spent in GC since program start
    81  		#+...+#      wall-clock/CPU times for the phases of the GC
    82  		#->#-># MB   heap size at GC start, at GC end, and live heap
    83  		# MB goal    goal heap size
    84  		# MB stacks  estimated scannable stack size
    85  		# MB globals scannable global size
    86  		# P          number of processors used
    87  	The phases are stop-the-world (STW) sweep termination, concurrent
    88  	mark and scan, and STW mark termination. The CPU times
    89  	for mark/scan are broken down in to assist time (GC performed in
    90  	line with allocation), background GC time, and idle GC time.
    91  	If the line ends with "(forced)", this GC was forced by a
    92  	runtime.GC() call.
    93  
    94  	harddecommit: setting harddecommit=1 causes memory that is returned to the OS to
    95  	also have protections removed on it. This is the only mode of operation on Windows,
    96  	but is helpful in debugging scavenger-related issues on other platforms. Currently,
    97  	only supported on Linux.
    98  
    99  	inittrace: setting inittrace=1 causes the runtime to emit a single line to standard
   100  	error for each package with init work, summarizing the execution time and memory
   101  	allocation. No information is printed for inits executed as part of plugin loading
   102  	and for packages without both user defined and compiler generated init work.
   103  	The format of this line is subject to change. Currently, it is:
   104  		init # @#ms, # ms clock, # bytes, # allocs
   105  	where the fields are as follows:
   106  		init #      the package name
   107  		@# ms       time in milliseconds when the init started since program start
   108  		# clock     wall-clock time for package initialization work
   109  		# bytes     memory allocated on the heap
   110  		# allocs    number of heap allocations
   111  
   112  	madvdontneed: setting madvdontneed=0 will use MADV_FREE
   113  	instead of MADV_DONTNEED on Linux when returning memory to the
   114  	kernel. This is more efficient, but means RSS numbers will
   115  	drop only when the OS is under memory pressure.
   116  
   117  	memprofilerate: setting memprofilerate=X will update the value of runtime.MemProfileRate.
   118  	When set to 0 memory profiling is disabled.  Refer to the description of
   119  	MemProfileRate for the default value.
   120  
   121  	invalidptr: invalidptr=1 (the default) causes the garbage collector and stack
   122  	copier to crash the program if an invalid pointer value (for example, 1)
   123  	is found in a pointer-typed location. Setting invalidptr=0 disables this check.
   124  	This should only be used as a temporary workaround to diagnose buggy code.
   125  	The real fix is to not store integers in pointer-typed locations.
   126  
   127  	sbrk: setting sbrk=1 replaces the memory allocator and garbage collector
   128  	with a trivial allocator that obtains memory from the operating system and
   129  	never reclaims any memory.
   130  
   131  	scavtrace: setting scavtrace=1 causes the runtime to emit a single line to standard
   132  	error, roughly once per GC cycle, summarizing the amount of work done by the
   133  	scavenger as well as the total amount of memory returned to the operating system
   134  	and an estimate of physical memory utilization. The format of this line is subject
   135  	to change, but currently it is:
   136  		scav # KiB work, # KiB total, #% util
   137  	where the fields are as follows:
   138  		# KiB work   the amount of memory returned to the OS since the last line
   139  		# KiB total  the total amount of memory returned to the OS
   140  		#% util      the fraction of all unscavenged memory which is in-use
   141  	If the line ends with "(forced)", then scavenging was forced by a
   142  	debug.FreeOSMemory() call.
   143  
   144  	scheddetail: setting schedtrace=X and scheddetail=1 causes the scheduler to emit
   145  	detailed multiline info every X milliseconds, describing state of the scheduler,
   146  	processors, threads and goroutines.
   147  
   148  	schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard
   149  	error every X milliseconds, summarizing the scheduler state.
   150  
   151  	tracebackancestors: setting tracebackancestors=N extends tracebacks with the stacks at
   152  	which goroutines were created, where N limits the number of ancestor goroutines to
   153  	report. This also extends the information returned by runtime.Stack. Ancestor's goroutine
   154  	IDs will refer to the ID of the goroutine at the time of creation; it's possible for this
   155  	ID to be reused for another goroutine. Setting N to 0 will report no ancestry information.
   156  
   157  	asyncpreemptoff: asyncpreemptoff=1 disables signal-based
   158  	asynchronous goroutine preemption. This makes some loops
   159  	non-preemptible for long periods, which may delay GC and
   160  	goroutine scheduling. This is useful for debugging GC issues
   161  	because it also disables the conservative stack scanning used
   162  	for asynchronously preempted goroutines.
   163  
   164  The net and net/http packages also refer to debugging variables in GODEBUG.
   165  See the documentation for those packages for details.
   166  
   167  The GOMAXPROCS variable limits the number of operating system threads that
   168  can execute user-level Go code simultaneously. There is no limit to the number of threads
   169  that can be blocked in system calls on behalf of Go code; those do not count against
   170  the GOMAXPROCS limit. This package's GOMAXPROCS function queries and changes
   171  the limit.
   172  
   173  The GORACE variable configures the race detector, for programs built using -race.
   174  See https://golang.org/doc/articles/race_detector.html for details.
   175  
   176  The GOTRACEBACK variable controls the amount of output generated when a Go
   177  program fails due to an unrecovered panic or an unexpected runtime condition.
   178  By default, a failure prints a stack trace for the current goroutine,
   179  eliding functions internal to the run-time system, and then exits with exit code 2.
   180  The failure prints stack traces for all goroutines if there is no current goroutine
   181  or the failure is internal to the run-time.
   182  GOTRACEBACK=none omits the goroutine stack traces entirely.
   183  GOTRACEBACK=single (the default) behaves as described above.
   184  GOTRACEBACK=all adds stack traces for all user-created goroutines.
   185  GOTRACEBACK=system is like “all” but adds stack frames for run-time functions
   186  and shows goroutines created internally by the run-time.
   187  GOTRACEBACK=crash is like “system” but crashes in an operating system-specific
   188  manner instead of exiting. For example, on Unix systems, the crash raises
   189  SIGABRT to trigger a core dump.
   190  For historical reasons, the GOTRACEBACK settings 0, 1, and 2 are synonyms for
   191  none, all, and system, respectively.
   192  The runtime/debug package's SetTraceback function allows increasing the
   193  amount of output at run time, but it cannot reduce the amount below that
   194  specified by the environment variable.
   195  See https://golang.org/pkg/runtime/debug/#SetTraceback.
   196  
   197  The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete
   198  the set of Go environment variables. They influence the building of Go programs
   199  (see https://golang.org/cmd/go and https://golang.org/pkg/go/build).
   200  GOARCH, GOOS, and GOROOT are recorded at compile time and made available by
   201  constants or functions in this package, but they do not influence the execution
   202  of the run-time system.
   203  */
   204  package runtime
   205  
   206  import (
   207  	"internal/goarch"
   208  	"internal/goos"
   209  )
   210  
   211  // Caller reports file and line number information about function invocations on
   212  // the calling goroutine's stack. The argument skip is the number of stack frames
   213  // to ascend, with 0 identifying the caller of Caller.  (For historical reasons the
   214  // meaning of skip differs between Caller and Callers.) The return values report the
   215  // program counter, file name, and line number within the file of the corresponding
   216  // call. The boolean ok is false if it was not possible to recover the information.
   217  func Caller(skip int) (pc uintptr, file string, line int, ok bool) {
   218  	rpc := make([]uintptr, 1)
   219  	n := callers(skip+1, rpc[:])
   220  	if n < 1 {
   221  		return
   222  	}
   223  	frame, _ := CallersFrames(rpc).Next()
   224  	return frame.PC, frame.File, frame.Line, frame.PC != 0
   225  }
   226  
   227  // Callers fills the slice pc with the return program counters of function invocations
   228  // on the calling goroutine's stack. The argument skip is the number of stack frames
   229  // to skip before recording in pc, with 0 identifying the frame for Callers itself and
   230  // 1 identifying the caller of Callers.
   231  // It returns the number of entries written to pc.
   232  //
   233  // To translate these PCs into symbolic information such as function
   234  // names and line numbers, use CallersFrames. CallersFrames accounts
   235  // for inlined functions and adjusts the return program counters into
   236  // call program counters. Iterating over the returned slice of PCs
   237  // directly is discouraged, as is using FuncForPC on any of the
   238  // returned PCs, since these cannot account for inlining or return
   239  // program counter adjustment.
   240  func Callers(skip int, pc []uintptr) int {
   241  	// runtime.callers uses pc.array==nil as a signal
   242  	// to print a stack trace. Pick off 0-length pc here
   243  	// so that we don't let a nil pc slice get to it.
   244  	if len(pc) == 0 {
   245  		return 0
   246  	}
   247  	return callers(skip, pc)
   248  }
   249  
   250  var defaultGOROOT string // set by cmd/link
   251  
   252  // GOROOT returns the root of the Go tree. It uses the
   253  // GOROOT environment variable, if set at process start,
   254  // or else the root used during the Go build.
   255  func GOROOT() string {
   256  	s := gogetenv("GOROOT")
   257  	if s != "" {
   258  		return s
   259  	}
   260  	return defaultGOROOT
   261  }
   262  
   263  // buildVersion is the Go tree's version string at build time.
   264  //
   265  // If any GOEXPERIMENTs are set to non-default values, it will include
   266  // "X:<GOEXPERIMENT>".
   267  //
   268  // This is set by the linker.
   269  //
   270  // This is accessed by "go version <binary>".
   271  var buildVersion string
   272  
   273  // Version returns the Go tree's version string.
   274  // It is either the commit hash and date at the time of the build or,
   275  // when possible, a release tag like "go1.3".
   276  func Version() string {
   277  	return buildVersion
   278  }
   279  
   280  // GOOS is the running program's operating system target:
   281  // one of darwin, freebsd, linux, and so on.
   282  // To view possible combinations of GOOS and GOARCH, run "go tool dist list".
   283  const GOOS string = goos.GOOS
   284  
   285  // GOARCH is the running program's architecture target:
   286  // one of 386, amd64, arm, s390x, and so on.
   287  const GOARCH string = goarch.GOARCH
   288  

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