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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		memprofilerate: setting memprofilerate=X will update the value of runtime.MemProfileRate.
    86		When set to 0 memory profiling is disabled.  Refer to the description of
    87		MemProfileRate for the default value.
    88	
    89		invalidptr: defaults to invalidptr=1, causing the garbage collector and stack
    90		copier to crash the program if an invalid pointer value (for example, 1)
    91		is found in a pointer-typed location. Setting invalidptr=0 disables this check.
    92		This should only be used as a temporary workaround to diagnose buggy code.
    93		The real fix is to not store integers in pointer-typed locations.
    94	
    95		sbrk: setting sbrk=1 replaces the memory allocator and garbage collector
    96		with a trivial allocator that obtains memory from the operating system and
    97		never reclaims any memory.
    98	
    99		scavenge: scavenge=1 enables debugging mode of heap scavenger.
   100	
   101		scheddetail: setting schedtrace=X and scheddetail=1 causes the scheduler to emit
   102		detailed multiline info every X milliseconds, describing state of the scheduler,
   103		processors, threads and goroutines.
   104	
   105		schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard
   106		error every X milliseconds, summarizing the scheduler state.
   107	
   108	The net and net/http packages also refer to debugging variables in GODEBUG.
   109	See the documentation for those packages for details.
   110	
   111	The GOMAXPROCS variable limits the number of operating system threads that
   112	can execute user-level Go code simultaneously. There is no limit to the number of threads
   113	that can be blocked in system calls on behalf of Go code; those do not count against
   114	the GOMAXPROCS limit. This package's GOMAXPROCS function queries and changes
   115	the limit.
   116	
   117	The GOTRACEBACK variable controls the amount of output generated when a Go
   118	program fails due to an unrecovered panic or an unexpected runtime condition.
   119	By default, a failure prints a stack trace for the current goroutine,
   120	eliding functions internal to the run-time system, and then exits with exit code 2.
   121	The failure prints stack traces for all goroutines if there is no current goroutine
   122	or the failure is internal to the run-time.
   123	GOTRACEBACK=none omits the goroutine stack traces entirely.
   124	GOTRACEBACK=single (the default) behaves as described above.
   125	GOTRACEBACK=all adds stack traces for all user-created goroutines.
   126	GOTRACEBACK=system is like ``all'' but adds stack frames for run-time functions
   127	and shows goroutines created internally by the run-time.
   128	GOTRACEBACK=crash is like ``system'' but crashes in an operating system-specific
   129	manner instead of exiting. For example, on Unix systems, the crash raises
   130	SIGABRT to trigger a core dump.
   131	For historical reasons, the GOTRACEBACK settings 0, 1, and 2 are synonyms for
   132	none, all, and system, respectively.
   133	The runtime/debug package's SetTraceback function allows increasing the
   134	amount of output at run time, but it cannot reduce the amount below that
   135	specified by the environment variable.
   136	See https://golang.org/pkg/runtime/debug/#SetTraceback.
   137	
   138	The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete
   139	the set of Go environment variables. They influence the building of Go programs
   140	(see https://golang.org/cmd/go and https://golang.org/pkg/go/build).
   141	GOARCH, GOOS, and GOROOT are recorded at compile time and made available by
   142	constants or functions in this package, but they do not influence the execution
   143	of the run-time system.
   144	*/
   145	package runtime
   146	
   147	import "runtime/internal/sys"
   148	
   149	// Caller reports file and line number information about function invocations on
   150	// the calling goroutine's stack.  The argument skip is the number of stack frames
   151	// to ascend, with 0 identifying the caller of Caller.  (For historical reasons the
   152	// meaning of skip differs between Caller and Callers.) The return values report the
   153	// program counter, file name, and line number within the file of the corresponding
   154	// call.  The boolean ok is false if it was not possible to recover the information.
   155	func Caller(skip int) (pc uintptr, file string, line int, ok bool) {
   156		// Ask for two PCs: the one we were asked for
   157		// and what it called, so that we can see if it
   158		// "called" sigpanic.
   159		var rpc [2]uintptr
   160		if callers(1+skip-1, rpc[:]) < 2 {
   161			return
   162		}
   163		f := findfunc(rpc[1])
   164		if f == nil {
   165			// TODO(rsc): Probably a bug?
   166			// The C version said "have retpc at least"
   167			// but actually returned pc=0.
   168			ok = true
   169			return
   170		}
   171		pc = rpc[1]
   172		xpc := pc
   173		g := findfunc(rpc[0])
   174		// All architectures turn faults into apparent calls to sigpanic.
   175		// If we see a call to sigpanic, we do not back up the PC to find
   176		// the line number of the call instruction, because there is no call.
   177		if xpc > f.entry && (g == nil || g.entry != funcPC(sigpanic)) {
   178			xpc--
   179		}
   180		file, line32 := funcline(f, xpc)
   181		line = int(line32)
   182		ok = true
   183		return
   184	}
   185	
   186	// Callers fills the slice pc with the return program counters of function invocations
   187	// on the calling goroutine's stack.  The argument skip is the number of stack frames
   188	// to skip before recording in pc, with 0 identifying the frame for Callers itself and
   189	// 1 identifying the caller of Callers.
   190	// It returns the number of entries written to pc.
   191	//
   192	// Note that since each slice entry pc[i] is a return program counter,
   193	// looking up the file and line for pc[i] (for example, using (*Func).FileLine)
   194	// will return the file and line number of the instruction immediately
   195	// following the call.
   196	// To look up the file and line number of the call itself, use pc[i]-1.
   197	// As an exception to this rule, if pc[i-1] corresponds to the function
   198	// runtime.sigpanic, then pc[i] is the program counter of a faulting
   199	// instruction and should be used without any subtraction.
   200	func Callers(skip int, pc []uintptr) int {
   201		// runtime.callers uses pc.array==nil as a signal
   202		// to print a stack trace.  Pick off 0-length pc here
   203		// so that we don't let a nil pc slice get to it.
   204		if len(pc) == 0 {
   205			return 0
   206		}
   207		return callers(skip, pc)
   208	}
   209	
   210	// GOROOT returns the root of the Go tree.
   211	// It uses the GOROOT environment variable, if set,
   212	// or else the root used during the Go build.
   213	func GOROOT() string {
   214		s := gogetenv("GOROOT")
   215		if s != "" {
   216			return s
   217		}
   218		return sys.DefaultGoroot
   219	}
   220	
   221	// Version returns the Go tree's version string.
   222	// It is either the commit hash and date at the time of the build or,
   223	// when possible, a release tag like "go1.3".
   224	func Version() string {
   225		return sys.TheVersion
   226	}
   227	
   228	// GOOS is the running program's operating system target:
   229	// one of darwin, freebsd, linux, and so on.
   230	const GOOS string = sys.TheGoos
   231	
   232	// GOARCH is the running program's architecture target:
   233	// 386, amd64, or arm.
   234	const GOARCH string = sys.TheGoarch
   235	

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