github.com/zach-klippenstein/go@v0.0.0-20150108044943-fcfbeb3adf58/src/runtime/extern.go (about) 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 http://golang.org/pkg/runtime/debug/#SetGCPercent. 23 24 The GODEBUG variable controls debug output from the runtime. GODEBUG value is 25 a comma-separated list of name=val pairs. Supported names are: 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 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. 33 34 gctrace: setting gctrace=1 causes the garbage collector to emit a single line to standard 35 error at each collection, summarizing the amount of memory collected and the 36 length of the pause. Setting gctrace=2 emits the same summary but also 37 repeats each collection. 38 39 gcdead: setting gcdead=1 causes the garbage collector to clobber all stack slots 40 that it thinks are dead. 41 42 invalidptr: defaults to invalidptr=1, causing the garbage collector and stack 43 copier to crash the program if an invalid pointer value (for example, 1) 44 is found in a pointer-typed location. Setting invalidptr=0 disables this check. 45 This should only be used as a temporary workaround to diagnose buggy code. 46 The real fix is to not store integers in pointer-typed locations. 47 48 scheddetail: setting schedtrace=X and scheddetail=1 causes the scheduler to emit 49 detailed multiline info every X milliseconds, describing state of the scheduler, 50 processors, threads and goroutines. 51 52 schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard 53 error every X milliseconds, summarizing the scheduler state. 54 55 scavenge: scavenge=1 enables debugging mode of heap scavenger. 56 57 wbshadow: setting wbshadow=1 enables a shadow copy of the heap 58 used to detect missing write barriers at the next write to a 59 given location. If a bug can be detected in this mode it is 60 typically easy to understand, since the crash says quite 61 clearly what kind of word has missed a write barrier. 62 Setting wbshadow=2 checks the shadow copy during garbage 63 collection as well. Bugs detected at garbage collection can be 64 difficult to understand, because there is no context for what 65 the found word means. Typically you have to reproduce the 66 problem with allocfreetrace=1 in order to understand the type 67 of the badly updated word. 68 69 The GOMAXPROCS variable limits the number of operating system threads that 70 can execute user-level Go code simultaneously. There is no limit to the number of threads 71 that can be blocked in system calls on behalf of Go code; those do not count against 72 the GOMAXPROCS limit. This package's GOMAXPROCS function queries and changes 73 the limit. 74 75 The GOTRACEBACK variable controls the amount of output generated when a Go 76 program fails due to an unrecovered panic or an unexpected runtime condition. 77 By default, a failure prints a stack trace for every extant goroutine, eliding functions 78 internal to the run-time system, and then exits with exit code 2. 79 If GOTRACEBACK=0, the per-goroutine stack traces are omitted entirely. 80 If GOTRACEBACK=1, the default behavior is used. 81 If GOTRACEBACK=2, the per-goroutine stack traces include run-time functions. 82 If GOTRACEBACK=crash, the per-goroutine stack traces include run-time functions, 83 and if possible the program crashes in an operating-specific manner instead of 84 exiting. For example, on Unix systems, the program raises SIGABRT to trigger a 85 core dump. 86 87 The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete 88 the set of Go environment variables. They influence the building of Go programs 89 (see http://golang.org/cmd/go and http://golang.org/pkg/go/build). 90 GOARCH, GOOS, and GOROOT are recorded at compile time and made available by 91 constants or functions in this package, but they do not influence the execution 92 of the run-time system. 93 */ 94 package runtime 95 96 // Caller reports file and line number information about function invocations on 97 // the calling goroutine's stack. The argument skip is the number of stack frames 98 // to ascend, with 0 identifying the caller of Caller. (For historical reasons the 99 // meaning of skip differs between Caller and Callers.) The return values report the 100 // program counter, file name, and line number within the file of the corresponding 101 // call. The boolean ok is false if it was not possible to recover the information. 102 func Caller(skip int) (pc uintptr, file string, line int, ok bool) { 103 // Ask for two PCs: the one we were asked for 104 // and what it called, so that we can see if it 105 // "called" sigpanic. 106 var rpc [2]uintptr 107 if callers(1+skip-1, &rpc[0], 2) < 2 { 108 return 109 } 110 f := findfunc(rpc[1]) 111 if f == nil { 112 // TODO(rsc): Probably a bug? 113 // The C version said "have retpc at least" 114 // but actually returned pc=0. 115 ok = true 116 return 117 } 118 pc = rpc[1] 119 xpc := pc 120 g := findfunc(rpc[0]) 121 // All architectures turn faults into apparent calls to sigpanic. 122 // If we see a call to sigpanic, we do not back up the PC to find 123 // the line number of the call instruction, because there is no call. 124 if xpc > f.entry && (g == nil || g.entry != funcPC(sigpanic)) { 125 xpc-- 126 } 127 file, line32 := funcline(f, xpc) 128 line = int(line32) 129 ok = true 130 return 131 } 132 133 // Callers fills the slice pc with the return program counters of function invocations 134 // on the calling goroutine's stack. The argument skip is the number of stack frames 135 // to skip before recording in pc, with 0 identifying the frame for Callers itself and 136 // 1 identifying the caller of Callers. 137 // It returns the number of entries written to pc. 138 // 139 // Note that since each slice entry pc[i] is a return program counter, 140 // looking up the file and line for pc[i] (for example, using (*Func).FileLine) 141 // will return the file and line number of the instruction immediately 142 // following the call. 143 // To look up the file and line number of the call itself, use pc[i]-1. 144 // As an exception to this rule, if pc[i-1] corresponds to the function 145 // runtime.sigpanic, then pc[i] is the program counter of a faulting 146 // instruction and should be used without any subtraction. 147 func Callers(skip int, pc []uintptr) int { 148 // runtime.callers uses pc.array==nil as a signal 149 // to print a stack trace. Pick off 0-length pc here 150 // so that we don't let a nil pc slice get to it. 151 if len(pc) == 0 { 152 return 0 153 } 154 return callers(skip, &pc[0], len(pc)) 155 } 156 157 // GOROOT returns the root of the Go tree. 158 // It uses the GOROOT environment variable, if set, 159 // or else the root used during the Go build. 160 func GOROOT() string { 161 s := gogetenv("GOROOT") 162 if s != "" { 163 return s 164 } 165 return defaultGoroot 166 } 167 168 // Version returns the Go tree's version string. 169 // It is either the commit hash and date at the time of the build or, 170 // when possible, a release tag like "go1.3". 171 func Version() string { 172 return theVersion 173 } 174 175 // GOOS is the running program's operating system target: 176 // one of darwin, freebsd, linux, and so on. 177 const GOOS string = theGoos 178 179 // GOARCH is the running program's architecture target: 180 // 386, amd64, or arm. 181 const GOARCH string = theGoarch