github.com/razvanm/vanadium-go-1.3@v0.0.0-20160721203343-4a65068e5915/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 scheddetail: setting schedtrace=X and scheddetail=1 causes the scheduler to emit 43 detailed multiline info every X milliseconds, describing state of the scheduler, 44 processors, threads and goroutines. 45 46 schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard 47 error every X milliseconds, summarizing the scheduler state. 48 49 scavenge: scavenge=1 enables debugging mode of heap scavenger. 50 51 The GOMAXPROCS variable limits the number of operating system threads that 52 can execute user-level Go code simultaneously. There is no limit to the number of threads 53 that can be blocked in system calls on behalf of Go code; those do not count against 54 the GOMAXPROCS limit. This package's GOMAXPROCS function queries and changes 55 the limit. 56 57 The GOTRACEBACK variable controls the amount of output generated when a Go 58 program fails due to an unrecovered panic or an unexpected runtime condition. 59 By default, a failure prints a stack trace for every extant goroutine, eliding functions 60 internal to the run-time system, and then exits with exit code 2. 61 If GOTRACEBACK=0, the per-goroutine stack traces are omitted entirely. 62 If GOTRACEBACK=1, the default behavior is used. 63 If GOTRACEBACK=2, the per-goroutine stack traces include run-time functions. 64 If GOTRACEBACK=crash, the per-goroutine stack traces include run-time functions, 65 and if possible the program crashes in an operating-specific manner instead of 66 exiting. For example, on Unix systems, the program raises SIGABRT to trigger a 67 core dump. 68 69 The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete 70 the set of Go environment variables. They influence the building of Go programs 71 (see http://golang.org/cmd/go and http://golang.org/pkg/go/build). 72 GOARCH, GOOS, and GOROOT are recorded at compile time and made available by 73 constants or functions in this package, but they do not influence the execution 74 of the run-time system. 75 */ 76 package runtime 77 78 // Caller reports file and line number information about function invocations on 79 // the calling goroutine's stack. The argument skip is the number of stack frames 80 // to ascend, with 0 identifying the caller of Caller. (For historical reasons the 81 // meaning of skip differs between Caller and Callers.) The return values report the 82 // program counter, file name, and line number within the file of the corresponding 83 // call. The boolean ok is false if it was not possible to recover the information. 84 func Caller(skip int) (pc uintptr, file string, line int, ok bool) { 85 // Ask for two PCs: the one we were asked for 86 // and what it called, so that we can see if it 87 // "called" sigpanic. 88 var rpc [2]uintptr 89 if callers(1+skip-1, &rpc[0], 2) < 2 { 90 return 91 } 92 f := findfunc(rpc[1]) 93 if f == nil { 94 // TODO(rsc): Probably a bug? 95 // The C version said "have retpc at least" 96 // but actually returned pc=0. 97 ok = true 98 return 99 } 100 pc = rpc[1] 101 xpc := pc 102 g := findfunc(rpc[0]) 103 // All architectures turn faults into apparent calls to sigpanic. 104 // If we see a call to sigpanic, we do not back up the PC to find 105 // the line number of the call instruction, because there is no call. 106 if xpc > f.entry && (g == nil || g.entry != funcPC(sigpanic)) { 107 xpc-- 108 } 109 line = int(funcline(f, xpc, &file)) 110 ok = true 111 return 112 } 113 114 // Callers fills the slice pc with the program counters of function invocations 115 // on the calling goroutine's stack. The argument skip is the number of stack frames 116 // to skip before recording in pc, with 0 identifying the frame for Callers itself and 117 // 1 identifying the caller of Callers. 118 // It returns the number of entries written to pc. 119 func Callers(skip int, pc []uintptr) int { 120 // runtime.callers uses pc.array==nil as a signal 121 // to print a stack trace. Pick off 0-length pc here 122 // so that we don't let a nil pc slice get to it. 123 if len(pc) == 0 { 124 return 0 125 } 126 return callers(skip, &pc[0], len(pc)) 127 } 128 129 // GOROOT returns the root of the Go tree. 130 // It uses the GOROOT environment variable, if set, 131 // or else the root used during the Go build. 132 func GOROOT() string { 133 s := gogetenv("GOROOT") 134 if s != "" { 135 return s 136 } 137 return defaultGoroot 138 } 139 140 // Version returns the Go tree's version string. 141 // It is either the commit hash and date at the time of the build or, 142 // when possible, a release tag like "go1.3". 143 func Version() string { 144 return theVersion 145 } 146 147 // GOOS is the running program's operating system target: 148 // one of darwin, freebsd, linux, and so on. 149 const GOOS string = theGoos 150 151 // GOARCH is the running program's architecture target: 152 // 386, amd64, or arm. 153 const GOARCH string = theGoarch