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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: defaults to invalidptr=1, causing 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  		# KiB work   the amount of memory returned to the OS since the last scav line
   110  		# KiB total  how much of the heap at this point in time has been released to the OS
   111  		#% util      the fraction of all unscavenged memory which is in-use
   112  	If the line ends with "(forced)", then scavenging was forced by a
   113  	debug.FreeOSMemory() call.
   114  
   115  	scheddetail: setting schedtrace=X and scheddetail=1 causes the scheduler to emit
   116  	detailed multiline info every X milliseconds, describing state of the scheduler,
   117  	processors, threads and goroutines.
   118  
   119  	schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard
   120  	error every X milliseconds, summarizing the scheduler state.
   121  
   122  	tracebackancestors: setting tracebackancestors=N extends tracebacks with the stacks at
   123  	which goroutines were created, where N limits the number of ancestor goroutines to
   124  	report. This also extends the information returned by runtime.Stack. Ancestor's goroutine
   125  	IDs will refer to the ID of the goroutine at the time of creation; it's possible for this
   126  	ID to be reused for another goroutine. Setting N to 0 will report no ancestry information.
   127  
   128  	asyncpreemptoff: asyncpreemptoff=1 disables signal-based
   129  	asynchronous goroutine preemption. This makes some loops
   130  	non-preemptible for long periods, which may delay GC and
   131  	goroutine scheduling. This is useful for debugging GC issues
   132  	because it also disables the conservative stack scanning used
   133  	for asynchronously preempted goroutines.
   134  
   135  The net, net/http, and crypto/tls packages also refer to debugging variables in GODEBUG.
   136  See the documentation for those packages for details.
   137  
   138  The GOMAXPROCS variable limits the number of operating system threads that
   139  can execute user-level Go code simultaneously. There is no limit to the number of threads
   140  that can be blocked in system calls on behalf of Go code; those do not count against
   141  the GOMAXPROCS limit. This package's GOMAXPROCS function queries and changes
   142  the limit.
   143  
   144  The GORACE variable configures the race detector, for programs built using -race.
   145  See https://golang.org/doc/articles/race_detector.html for details.
   146  
   147  The GOTRACEBACK variable controls the amount of output generated when a Go
   148  program fails due to an unrecovered panic or an unexpected runtime condition.
   149  By default, a failure prints a stack trace for the current goroutine,
   150  eliding functions internal to the run-time system, and then exits with exit code 2.
   151  The failure prints stack traces for all goroutines if there is no current goroutine
   152  or the failure is internal to the run-time.
   153  GOTRACEBACK=none omits the goroutine stack traces entirely.
   154  GOTRACEBACK=single (the default) behaves as described above.
   155  GOTRACEBACK=all adds stack traces for all user-created goroutines.
   156  GOTRACEBACK=system is like ``all'' but adds stack frames for run-time functions
   157  and shows goroutines created internally by the run-time.
   158  GOTRACEBACK=crash is like ``system'' but crashes in an operating system-specific
   159  manner instead of exiting. For example, on Unix systems, the crash raises
   160  SIGABRT to trigger a core dump.
   161  For historical reasons, the GOTRACEBACK settings 0, 1, and 2 are synonyms for
   162  none, all, and system, respectively.
   163  The runtime/debug package's SetTraceback function allows increasing the
   164  amount of output at run time, but it cannot reduce the amount below that
   165  specified by the environment variable.
   166  See https://golang.org/pkg/runtime/debug/#SetTraceback.
   167  
   168  The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete
   169  the set of Go environment variables. They influence the building of Go programs
   170  (see https://golang.org/cmd/go and https://golang.org/pkg/go/build).
   171  GOARCH, GOOS, and GOROOT are recorded at compile time and made available by
   172  constants or functions in this package, but they do not influence the execution
   173  of the run-time system.
   174  */
   175  package runtime
   176  
   177  import "runtime/internal/sys"
   178  
   179  // Caller reports file and line number information about function invocations on
   180  // the calling goroutine's stack. The argument skip is the number of stack frames
   181  // to ascend, with 0 identifying the caller of Caller.  (For historical reasons the
   182  // meaning of skip differs between Caller and Callers.) The return values report the
   183  // program counter, file name, and line number within the file of the corresponding
   184  // call. The boolean ok is false if it was not possible to recover the information.
   185  func Caller(skip int) (pc uintptr, file string, line int, ok bool) {
   186  	rpc := make([]uintptr, 1)
   187  	n := callers(skip+1, rpc[:])
   188  	if n < 1 {
   189  		return
   190  	}
   191  	frame, _ := CallersFrames(rpc).Next()
   192  	return frame.PC, frame.File, frame.Line, frame.PC != 0
   193  }
   194  
   195  // Callers fills the slice pc with the return program counters of function invocations
   196  // on the calling goroutine's stack. The argument skip is the number of stack frames
   197  // to skip before recording in pc, with 0 identifying the frame for Callers itself and
   198  // 1 identifying the caller of Callers.
   199  // It returns the number of entries written to pc.
   200  //
   201  // To translate these PCs into symbolic information such as function
   202  // names and line numbers, use CallersFrames. CallersFrames accounts
   203  // for inlined functions and adjusts the return program counters into
   204  // call program counters. Iterating over the returned slice of PCs
   205  // directly is discouraged, as is using FuncForPC on any of the
   206  // returned PCs, since these cannot account for inlining or return
   207  // program counter adjustment.
   208  func Callers(skip int, pc []uintptr) int {
   209  	// runtime.callers uses pc.array==nil as a signal
   210  	// to print a stack trace. Pick off 0-length pc here
   211  	// so that we don't let a nil pc slice get to it.
   212  	if len(pc) == 0 {
   213  		return 0
   214  	}
   215  	return callers(skip, pc)
   216  }
   217  
   218  // GOROOT returns the root of the Go tree. It uses the
   219  // GOROOT environment variable, if set at process start,
   220  // or else the root used during the Go build.
   221  func GOROOT() string {
   222  	s := gogetenv("GOROOT")
   223  	if s != "" {
   224  		return s
   225  	}
   226  	return sys.DefaultGoroot
   227  }
   228  
   229  // Version returns the Go tree's version string.
   230  // It is either the commit hash and date at the time of the build or,
   231  // when possible, a release tag like "go1.3".
   232  func Version() string {
   233  	return sys.TheVersion
   234  }
   235  
   236  // GOOS is the running program's operating system target:
   237  // one of darwin, freebsd, linux, and so on.
   238  // To view possible combinations of GOOS and GOARCH, run "go tool dist list".
   239  const GOOS string = sys.GOOS
   240  
   241  // GOARCH is the running program's architecture target:
   242  // one of 386, amd64, arm, s390x, and so on.
   243  const GOARCH string = sys.GOARCH
   244  

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