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

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