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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	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		cgocheck: setting cgocheck=0 disables all checks for packages
    31		using cgo to incorrectly pass Go pointers to non-Go code.
    32		Setting cgocheck=1 (the default) enables relatively cheap
    33		checks that may miss some errors.  Setting cgocheck=2 enables
    34		expensive checks that should not miss any errors, but will
    35		cause your program to run slower.
    36	
    37		efence: setting efence=1 causes the allocator to run in a mode
    38		where each object is allocated on a unique page and addresses are
    39		never recycled.
    40	
    41		gccheckmark: setting gccheckmark=1 enables verification of the
    42		garbage collector's concurrent mark phase by performing a
    43		second mark pass while the world is stopped.  If the second
    44		pass finds a reachable object that was not found by concurrent
    45		mark, the garbage collector will panic.
    46	
    47		gcpacertrace: setting gcpacertrace=1 causes the garbage collector to
    48		print information about the internal state of the concurrent pacer.
    49	
    50		gcshrinkstackoff: setting gcshrinkstackoff=1 disables moving goroutines
    51		onto smaller stacks. In this mode, a goroutine's stack can only grow.
    52	
    53		gcstackbarrieroff: setting gcstackbarrieroff=1 disables the use of stack barriers
    54		that allow the garbage collector to avoid repeating a stack scan during the
    55		mark termination phase.
    56	
    57		gcstackbarrierall: setting gcstackbarrierall=1 installs stack barriers
    58		in every stack frame, rather than in exponentially-spaced frames.
    59	
    60		gcstoptheworld: setting gcstoptheworld=1 disables concurrent garbage collection,
    61		making every garbage collection a stop-the-world event. Setting gcstoptheworld=2
    62		also disables concurrent sweeping after the garbage collection finishes.
    63	
    64		gctrace: setting gctrace=1 causes the garbage collector to emit a single line to standard
    65		error at each collection, summarizing the amount of memory collected and the
    66		length of the pause. Setting gctrace=2 emits the same summary but also
    67		repeats each collection. The format of this line is subject to change.
    68		Currently, it is:
    69			gc # @#s #%: #+#+# ms clock, #+#/#/#+# ms cpu, #->#-># MB, # MB goal, # P
    70		where the fields are as follows:
    71			gc #        the GC number, incremented at each GC
    72			@#s         time in seconds since program start
    73			#%          percentage of time spent in GC since program start
    74			#+...+#     wall-clock/CPU times for the phases of the GC
    75			#->#-># MB  heap size at GC start, at GC end, and live heap
    76			# MB goal   goal heap size
    77			# P         number of processors used
    78		The phases are stop-the-world (STW) sweep termination, concurrent
    79		mark and scan, and STW mark termination. The CPU times
    80		for mark/scan are broken down in to assist time (GC performed in
    81		line with allocation), background GC time, and idle GC time.
    82		If the line ends with "(forced)", this GC was forced by a
    83		runtime.GC() call and all phases are STW.
    84	
    85		Setting gctrace to any value > 0 also causes the garbage collector
    86		to emit a summary when memory is released back to the system.
    87		This process of returning memory to the system is called scavenging.
    88		The format of this summary is subject to change.
    89		Currently it is:
    90			scvg#: # MB released  printed only if non-zero
    91			scvg#: inuse: # idle: # sys: # released: # consumed: # (MB)
    92		where the fields are as follows:
    93			scvg#        the scavenge cycle number, incremented at each scavenge
    94			inuse: #     MB used or partially used spans
    95			idle: #      MB spans pending scavenging
    96			sys: #       MB mapped from the system
    97			released: #  MB released to the system
    98			consumed: #  MB allocated from the system
    99	
   100		memprofilerate: setting memprofilerate=X will update the value of runtime.MemProfileRate.
   101		When set to 0 memory profiling is disabled.  Refer to the description of
   102		MemProfileRate for the default value.
   103	
   104		invalidptr: defaults to invalidptr=1, causing the garbage collector and stack
   105		copier to crash the program if an invalid pointer value (for example, 1)
   106		is found in a pointer-typed location. Setting invalidptr=0 disables this check.
   107		This should only be used as a temporary workaround to diagnose buggy code.
   108		The real fix is to not store integers in pointer-typed locations.
   109	
   110		sbrk: setting sbrk=1 replaces the memory allocator and garbage collector
   111		with a trivial allocator that obtains memory from the operating system and
   112		never reclaims any memory.
   113	
   114		scavenge: scavenge=1 enables debugging mode of heap scavenger.
   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	The net and net/http packages also refer to debugging variables in GODEBUG.
   124	See the documentation for those packages for details.
   125	
   126	The GOMAXPROCS variable limits the number of operating system threads that
   127	can execute user-level Go code simultaneously. There is no limit to the number of threads
   128	that can be blocked in system calls on behalf of Go code; those do not count against
   129	the GOMAXPROCS limit. This package's GOMAXPROCS function queries and changes
   130	the limit.
   131	
   132	The GOTRACEBACK variable controls the amount of output generated when a Go
   133	program fails due to an unrecovered panic or an unexpected runtime condition.
   134	By default, a failure prints a stack trace for the current goroutine,
   135	eliding functions internal to the run-time system, and then exits with exit code 2.
   136	The failure prints stack traces for all goroutines if there is no current goroutine
   137	or the failure is internal to the run-time.
   138	GOTRACEBACK=none omits the goroutine stack traces entirely.
   139	GOTRACEBACK=single (the default) behaves as described above.
   140	GOTRACEBACK=all adds stack traces for all user-created goroutines.
   141	GOTRACEBACK=system is like ``all'' but adds stack frames for run-time functions
   142	and shows goroutines created internally by the run-time.
   143	GOTRACEBACK=crash is like ``system'' but crashes in an operating system-specific
   144	manner instead of exiting. For example, on Unix systems, the crash raises
   145	SIGABRT to trigger a core dump.
   146	For historical reasons, the GOTRACEBACK settings 0, 1, and 2 are synonyms for
   147	none, all, and system, respectively.
   148	The runtime/debug package's SetTraceback function allows increasing the
   149	amount of output at run time, but it cannot reduce the amount below that
   150	specified by the environment variable.
   151	See https://golang.org/pkg/runtime/debug/#SetTraceback.
   152	
   153	The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete
   154	the set of Go environment variables. They influence the building of Go programs
   155	(see https://golang.org/cmd/go and https://golang.org/pkg/go/build).
   156	GOARCH, GOOS, and GOROOT are recorded at compile time and made available by
   157	constants or functions in this package, but they do not influence the execution
   158	of the run-time system.
   159	*/
   160	package runtime
   161	
   162	import "runtime/internal/sys"
   163	
   164	// Caller reports file and line number information about function invocations on
   165	// the calling goroutine's stack. The argument skip is the number of stack frames
   166	// to ascend, with 0 identifying the caller of Caller.  (For historical reasons the
   167	// meaning of skip differs between Caller and Callers.) The return values report the
   168	// program counter, file name, and line number within the file of the corresponding
   169	// call. The boolean ok is false if it was not possible to recover the information.
   170	func Caller(skip int) (pc uintptr, file string, line int, ok bool) {
   171		// Ask for two PCs: the one we were asked for
   172		// and what it called, so that we can see if it
   173		// "called" sigpanic.
   174		var rpc [2]uintptr
   175		if callers(1+skip-1, rpc[:]) < 2 {
   176			return
   177		}
   178		f := findfunc(rpc[1])
   179		if f == nil {
   180			// TODO(rsc): Probably a bug?
   181			// The C version said "have retpc at least"
   182			// but actually returned pc=0.
   183			ok = true
   184			return
   185		}
   186		pc = rpc[1]
   187		xpc := pc
   188		g := findfunc(rpc[0])
   189		// All architectures turn faults into apparent calls to sigpanic.
   190		// If we see a call to sigpanic, we do not back up the PC to find
   191		// the line number of the call instruction, because there is no call.
   192		if xpc > f.entry && (g == nil || g.entry != funcPC(sigpanic)) {
   193			xpc--
   194		}
   195		file, line32 := funcline(f, xpc)
   196		line = int(line32)
   197		ok = true
   198		return
   199	}
   200	
   201	// Callers fills the slice pc with the return program counters of function invocations
   202	// on the calling goroutine's stack. The argument skip is the number of stack frames
   203	// to skip before recording in pc, with 0 identifying the frame for Callers itself and
   204	// 1 identifying the caller of Callers.
   205	// It returns the number of entries written to pc.
   206	//
   207	// Note that since each slice entry pc[i] is a return program counter,
   208	// looking up the file and line for pc[i] (for example, using (*Func).FileLine)
   209	// will normally return the file and line number of the instruction immediately
   210	// following the call.
   211	// To easily look up file/line information for the call sequence, use Frames.
   212	func Callers(skip int, pc []uintptr) int {
   213		// runtime.callers uses pc.array==nil as a signal
   214		// to print a stack trace. Pick off 0-length pc here
   215		// so that we don't let a nil pc slice get to it.
   216		if len(pc) == 0 {
   217			return 0
   218		}
   219		return callers(skip, pc)
   220	}
   221	
   222	// GOROOT returns the root of the Go tree.
   223	// It uses the GOROOT environment variable, if set,
   224	// or else the root used during the Go build.
   225	func GOROOT() string {
   226		s := gogetenv("GOROOT")
   227		if s != "" {
   228			return s
   229		}
   230		return sys.DefaultGoroot
   231	}
   232	
   233	// Version returns the Go tree's version string.
   234	// It is either the commit hash and date at the time of the build or,
   235	// when possible, a release tag like "go1.3".
   236	func Version() string {
   237		return sys.TheVersion
   238	}
   239	
   240	// GOOS is the running program's operating system target:
   241	// one of darwin, freebsd, linux, and so on.
   242	const GOOS string = sys.GOOS
   243	
   244	// GOARCH is the running program's architecture target:
   245	// 386, amd64, arm, or s390x.
   246	const GOARCH string = sys.GOARCH
   247	

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