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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.
     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  	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.
    33  
    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.
    40  
    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.
    44  
    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.
    50  
    51  	gcpacertrace: setting gcpacertrace=1 causes the garbage collector to
    52  	print information about the internal state of the concurrent pacer.
    53  
    54  	gcshrinkstackoff: setting gcshrinkstackoff=1 disables moving goroutines
    55  	onto smaller stacks. In this mode, a goroutine's stack can only grow.
    56  
    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.
    60  
    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.
    80  
    81  	madvdontneed: setting madvdontneed=1 will use MADV_DONTNEED
    82  	instead of MADV_FREE on Linux when returning memory to the
    83  	kernel. This is less efficient, but causes RSS numbers to drop
    84  	more quickly.
    85  
    86  	memprofilerate: setting memprofilerate=X will update the value of runtime.MemProfileRate.
    87  	When set to 0 memory profiling is disabled.  Refer to the description of
    88  	MemProfileRate for the default value.
    89  
    90  	invalidptr: invalidptr=1 (the default) causes the garbage collector and stack
    91  	copier to crash the program if an invalid pointer value (for example, 1)
    92  	is found in a pointer-typed location. Setting invalidptr=0 disables this check.
    93  	This should only be used as a temporary workaround to diagnose buggy code.
    94  	The real fix is to not store integers in pointer-typed locations.
    95  
    96  	sbrk: setting sbrk=1 replaces the memory allocator and garbage collector
    97  	with a trivial allocator that obtains memory from the operating system and
    98  	never reclaims any memory.
    99  
   100  	scavenge: scavenge=1 enables debugging mode of heap scavenger.
   101  
   102  	scavtrace: setting scavtrace=1 causes the runtime to emit a single line to standard
   103  	error, roughly once per GC cycle, summarizing the amount of work done by the
   104  	scavenger as well as the total amount of memory returned to the operating system
   105  	and an estimate of physical memory utilization. The format of this line is subject
   106  	to change, but currently it is:
   107  		scav # # KiB work, # KiB total, #% util
   108  	where the fields are as follows:
   109  		scav #       the scavenge cycle number
   110  		# KiB work   the amount of memory returned to the OS since the last line
   111  		# KiB total  the total amount of memory returned to the OS
   112  		#% util      the fraction of all unscavenged memory which is in-use
   113  	If the line ends with "(forced)", then scavenging was forced by a
   114  	debug.FreeOSMemory() call.
   115  
   116  	scheddetail: setting schedtrace=X and scheddetail=1 causes the scheduler to emit
   117  	detailed multiline info every X milliseconds, describing state of the scheduler,
   118  	processors, threads and goroutines.
   119  
   120  	schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard
   121  	error every X milliseconds, summarizing the scheduler state.
   122  
   123  	tracebackancestors: setting tracebackancestors=N extends tracebacks with the stacks at
   124  	which goroutines were created, where N limits the number of ancestor goroutines to
   125  	report. This also extends the information returned by runtime.Stack. Ancestor's goroutine
   126  	IDs will refer to the ID of the goroutine at the time of creation; it's possible for this
   127  	ID to be reused for another goroutine. Setting N to 0 will report no ancestry information.
   128  
   129  	asyncpreemptoff: asyncpreemptoff=1 disables signal-based
   130  	asynchronous goroutine preemption. This makes some loops
   131  	non-preemptible for long periods, which may delay GC and
   132  	goroutine scheduling. This is useful for debugging GC issues
   133  	because it also disables the conservative stack scanning used
   134  	for asynchronously preempted goroutines.
   135  
   136  The net, net/http, and crypto/tls packages also refer to debugging variables in GODEBUG.
   137  See the documentation for those packages for details.
   138  
   139  The GOMAXPROCS variable limits the number of operating system threads that
   140  can execute user-level Go code simultaneously. There is no limit to the number of threads
   141  that can be blocked in system calls on behalf of Go code; those do not count against
   142  the GOMAXPROCS limit. This package's GOMAXPROCS function queries and changes
   143  the limit.
   144  
   145  The GORACE variable configures the race detector, for programs built using -race.
   146  See https://golang.org/doc/articles/race_detector.html for details.
   147  
   148  The GOTRACEBACK variable controls the amount of output generated when a Go
   149  program fails due to an unrecovered panic or an unexpected runtime condition.
   150  By default, a failure prints a stack trace for the current goroutine,
   151  eliding functions internal to the run-time system, and then exits with exit code 2.
   152  The failure prints stack traces for all goroutines if there is no current goroutine
   153  or the failure is internal to the run-time.
   154  GOTRACEBACK=none omits the goroutine stack traces entirely.
   155  GOTRACEBACK=single (the default) behaves as described above.
   156  GOTRACEBACK=all adds stack traces for all user-created goroutines.
   157  GOTRACEBACK=system is like ``all'' but adds stack frames for run-time functions
   158  and shows goroutines created internally by the run-time.
   159  GOTRACEBACK=crash is like ``system'' but crashes in an operating system-specific
   160  manner instead of exiting. For example, on Unix systems, the crash raises
   161  SIGABRT to trigger a core dump.
   162  For historical reasons, the GOTRACEBACK settings 0, 1, and 2 are synonyms for
   163  none, all, and system, respectively.
   164  The runtime/debug package's SetTraceback function allows increasing the
   165  amount of output at run time, but it cannot reduce the amount below that
   166  specified by the environment variable.
   167  See https://golang.org/pkg/runtime/debug/#SetTraceback.
   168  
   169  The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete
   170  the set of Go environment variables. They influence the building of Go programs
   171  (see https://golang.org/cmd/go and https://golang.org/pkg/go/build).
   172  GOARCH, GOOS, and GOROOT are recorded at compile time and made available by
   173  constants or functions in this package, but they do not influence the execution
   174  of the run-time system.
   175  */
   176  package runtime
   177  
   178  import "runtime/internal/sys"
   179  
   180  // Caller reports file and line number information about function invocations on
   181  // the calling goroutine's stack. The argument skip is the number of stack frames
   182  // to ascend, with 0 identifying the caller of Caller.  (For historical reasons the
   183  // meaning of skip differs between Caller and Callers.) The return values report the
   184  // program counter, file name, and line number within the file of the corresponding
   185  // call. The boolean ok is false if it was not possible to recover the information.
   186  func Caller(skip int) (pc uintptr, file string, line int, ok bool) {
   187  	rpc := make([]uintptr, 1)
   188  	n := callers(skip+1, rpc[:])
   189  	if n < 1 {
   190  		return
   191  	}
   192  	frame, _ := CallersFrames(rpc).Next()
   193  	return frame.PC, frame.File, frame.Line, frame.PC != 0
   194  }
   195  
   196  // Callers fills the slice pc with the return program counters of function invocations
   197  // on the calling goroutine's stack. The argument skip is the number of stack frames
   198  // to skip before recording in pc, with 0 identifying the frame for Callers itself and
   199  // 1 identifying the caller of Callers.
   200  // It returns the number of entries written to pc.
   201  //
   202  // To translate these PCs into symbolic information such as function
   203  // names and line numbers, use CallersFrames. CallersFrames accounts
   204  // for inlined functions and adjusts the return program counters into
   205  // call program counters. Iterating over the returned slice of PCs
   206  // directly is discouraged, as is using FuncForPC on any of the
   207  // returned PCs, since these cannot account for inlining or return
   208  // program counter adjustment.
   209  func Callers(skip int, pc []uintptr) int {
   210  	// runtime.callers uses pc.array==nil as a signal
   211  	// to print a stack trace. Pick off 0-length pc here
   212  	// so that we don't let a nil pc slice get to it.
   213  	if len(pc) == 0 {
   214  		return 0
   215  	}
   216  	return callers(skip, pc)
   217  }
   218  
   219  // GOROOT returns the root of the Go tree. It uses the
   220  // GOROOT environment variable, if set at process start,
   221  // or else the root used during the Go build.
   222  func GOROOT() string {
   223  	s := gogetenv("GOROOT")
   224  	if s != "" {
   225  		return s
   226  	}
   227  	return sys.DefaultGoroot
   228  }
   229  
   230  // Version returns the Go tree's version string.
   231  // It is either the commit hash and date at the time of the build or,
   232  // when possible, a release tag like "go1.3".
   233  func Version() string {
   234  	return sys.TheVersion
   235  }
   236  
   237  // GOOS is the running program's operating system target:
   238  // one of darwin, freebsd, linux, and so on.
   239  // To view possible combinations of GOOS and GOARCH, run "go tool dist list".
   240  const GOOS string = sys.GOOS
   241  
   242  // GOARCH is the running program's architecture target:
   243  // one of 386, amd64, arm, s390x, and so on.
   244  const GOARCH string = sys.GOARCH
   245  

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