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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.
     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.
    11	Environment Variables
    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.
    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.
    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:
    27		allocfreetrace: setting allocfreetrace=1 causes every allocation to be
    28		profiled and a stack trace printed on each object's allocation and free.
    30		efence: setting efence=1 causes the allocator to run in a mode
    31		where each object is allocated on a unique page and addresses are
    32		never recycled.
    34		gccheckmark: setting gccheckmark=1 enables verification of the
    35		garbage collector's concurrent mark phase by performing a
    36		second mark pass while the world is stopped.  If the second
    37		pass finds a reachable object that was not found by concurrent
    38		mark, the garbage collector will panic.
    40		gcpacertrace: setting gcpacertrace=1 causes the garbage collector to
    41		print information about the internal state of the concurrent pacer.
    43		gcshrinkstackoff: setting gcshrinkstackoff=1 disables moving goroutines
    44		onto smaller stacks. In this mode, a goroutine's stack can only grow.
    46		gcstackbarrieroff: setting gcstackbarrieroff=1 disables the use of stack barriers
    47		that allow the garbage collector to avoid repeating a stack scan during the
    48		mark termination phase.
    50		gcstackbarrierall: setting gcstackbarrierall=1 installs stack barriers
    51		in every stack frame, rather than in exponentially-spaced frames.
    53		gcstoptheworld: setting gcstoptheworld=1 disables concurrent garbage collection,
    54		making every garbage collection a stop-the-world event. Setting gcstoptheworld=2
    55		also disables concurrent sweeping after the garbage collection finishes.
    57		gctrace: setting gctrace=1 causes the garbage collector to emit a single line to standard
    58		error at each collection, summarizing the amount of memory collected and the
    59		length of the pause. Setting gctrace=2 emits the same summary but also
    60		repeats each collection. The format of this line is subject to change.
    61		Currently, it is:
    62			gc # @#s #%: #+...+# ms clock, #+...+# ms cpu, #->#-># MB, # MB goal, # P
    63		where the fields are as follows:
    64			gc #        the GC number, incremented at each GC
    65			@#s         time in seconds since program start
    66			#%          percentage of time spent in GC since program start
    67			#+...+#     wall-clock/CPU times for the phases of the GC
    68			#->#-># MB  heap size at GC start, at GC end, and live heap
    69			# MB goal   goal heap size
    70			# P         number of processors used
    71		The phases are stop-the-world (STW) sweep termination, scan,
    72		synchronize Ps, mark, and STW mark termination. The CPU times
    73		for mark are broken down in to assist time (GC performed in
    74		line with allocation), background GC time, and idle GC time.
    75		If the line ends with "(forced)", this GC was forced by a
    76		runtime.GC() call and all phases are STW.
    78		memprofilerate: setting memprofilerate=X will update the value of runtime.MemProfileRate.
    79		When set to 0 memory profiling is disabled.  Refer to the description of
    80		MemProfileRate for the default value.
    82		invalidptr: defaults to invalidptr=1, causing the garbage collector and stack
    83		copier to crash the program if an invalid pointer value (for example, 1)
    84		is found in a pointer-typed location. Setting invalidptr=0 disables this check.
    85		This should only be used as a temporary workaround to diagnose buggy code.
    86		The real fix is to not store integers in pointer-typed locations.
    88		sbrk: setting sbrk=1 replaces the memory allocator and garbage collector
    89		with a trivial allocator that obtains memory from the operating system and
    90		never reclaims any memory.
    92		scavenge: scavenge=1 enables debugging mode of heap scavenger.
    94		scheddetail: setting schedtrace=X and scheddetail=1 causes the scheduler to emit
    95		detailed multiline info every X milliseconds, describing state of the scheduler,
    96		processors, threads and goroutines.
    98		schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard
    99		error every X milliseconds, summarizing the scheduler state.
   101	The GOMAXPROCS variable limits the number of operating system threads that
   102	can execute user-level Go code simultaneously. There is no limit to the number of threads
   103	that can be blocked in system calls on behalf of Go code; those do not count against
   104	the GOMAXPROCS limit. This package's GOMAXPROCS function queries and changes
   105	the limit.
   107	The GOTRACEBACK variable controls the amount of output generated when a Go
   108	program fails due to an unrecovered panic or an unexpected runtime condition.
   109	By default, a failure prints a stack trace for every extant goroutine, eliding functions
   110	internal to the run-time system, and then exits with exit code 2.
   111	If GOTRACEBACK=0, the per-goroutine stack traces are omitted entirely.
   112	If GOTRACEBACK=1, the default behavior is used.
   113	If GOTRACEBACK=2, the per-goroutine stack traces include run-time functions.
   114	If GOTRACEBACK=crash, the per-goroutine stack traces include run-time functions,
   115	and if possible the program crashes in an operating-specific manner instead of
   116	exiting. For example, on Unix systems, the program raises SIGABRT to trigger a
   117	core dump.
   119	The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete
   120	the set of Go environment variables. They influence the building of Go programs
   121	(see https://golang.org/cmd/go and https://golang.org/pkg/go/build).
   122	GOARCH, GOOS, and GOROOT are recorded at compile time and made available by
   123	constants or functions in this package, but they do not influence the execution
   124	of the run-time system.
   125	*/
   126	package runtime
   128	// Caller reports file and line number information about function invocations on
   129	// the calling goroutine's stack.  The argument skip is the number of stack frames
   130	// to ascend, with 0 identifying the caller of Caller.  (For historical reasons the
   131	// meaning of skip differs between Caller and Callers.) The return values report the
   132	// program counter, file name, and line number within the file of the corresponding
   133	// call.  The boolean ok is false if it was not possible to recover the information.
   134	func Caller(skip int) (pc uintptr, file string, line int, ok bool) {
   135		// Ask for two PCs: the one we were asked for
   136		// and what it called, so that we can see if it
   137		// "called" sigpanic.
   138		var rpc [2]uintptr
   139		if callers(1+skip-1, rpc[:]) < 2 {
   140			return
   141		}
   142		f := findfunc(rpc[1])
   143		if f == nil {
   144			// TODO(rsc): Probably a bug?
   145			// The C version said "have retpc at least"
   146			// but actually returned pc=0.
   147			ok = true
   148			return
   149		}
   150		pc = rpc[1]
   151		xpc := pc
   152		g := findfunc(rpc[0])
   153		// All architectures turn faults into apparent calls to sigpanic.
   154		// If we see a call to sigpanic, we do not back up the PC to find
   155		// the line number of the call instruction, because there is no call.
   156		if xpc > f.entry && (g == nil || g.entry != funcPC(sigpanic)) {
   157			xpc--
   158		}
   159		file, line32 := funcline(f, xpc)
   160		line = int(line32)
   161		ok = true
   162		return
   163	}
   165	// Callers fills the slice pc with the return program counters of function invocations
   166	// on the calling goroutine's stack.  The argument skip is the number of stack frames
   167	// to skip before recording in pc, with 0 identifying the frame for Callers itself and
   168	// 1 identifying the caller of Callers.
   169	// It returns the number of entries written to pc.
   170	//
   171	// Note that since each slice entry pc[i] is a return program counter,
   172	// looking up the file and line for pc[i] (for example, using (*Func).FileLine)
   173	// will return the file and line number of the instruction immediately
   174	// following the call.
   175	// To look up the file and line number of the call itself, use pc[i]-1.
   176	// As an exception to this rule, if pc[i-1] corresponds to the function
   177	// runtime.sigpanic, then pc[i] is the program counter of a faulting
   178	// instruction and should be used without any subtraction.
   179	func Callers(skip int, pc []uintptr) int {
   180		// runtime.callers uses pc.array==nil as a signal
   181		// to print a stack trace.  Pick off 0-length pc here
   182		// so that we don't let a nil pc slice get to it.
   183		if len(pc) == 0 {
   184			return 0
   185		}
   186		return callers(skip, pc)
   187	}
   189	// GOROOT returns the root of the Go tree.
   190	// It uses the GOROOT environment variable, if set,
   191	// or else the root used during the Go build.
   192	func GOROOT() string {
   193		s := gogetenv("GOROOT")
   194		if s != "" {
   195			return s
   196		}
   197		return defaultGoroot
   198	}
   200	// Version returns the Go tree's version string.
   201	// It is either the commit hash and date at the time of the build or,
   202	// when possible, a release tag like "go1.3".
   203	func Version() string {
   204		return theVersion
   205	}
   207	// GOOS is the running program's operating system target:
   208	// one of darwin, freebsd, linux, and so on.
   209	const GOOS string = theGoos
   211	// GOARCH is the running program's architecture target:
   212	// 386, amd64, or arm.
   213	const GOARCH string = theGoarch

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