// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

/* Package runtime contains operations that interact with Go's runtime system, such as functions to control goroutines. It also includes the low-level type information used by the reflect package; see reflect's documentation for the programmable interface to the run-time type system. Environment Variables The following environment variables ($name or %name%, depending on the host operating system) control the run-time behavior of Go programs. The meanings and use may change from release to release. The GOGC variable sets the initial garbage collection target percentage. A collection is triggered when the ratio of freshly allocated data to live data remaining after the previous collection reaches this percentage. The default is GOGC=100. Setting GOGC=off disables the garbage collector entirely. The runtime/debug package's SetGCPercent function allows changing this percentage at run time. See https://golang.org/pkg/runtime/debug/#SetGCPercent. The GODEBUG variable controls debugging variables within the runtime. It is a comma-separated list of name=val pairs setting these named variables: allocfreetrace: setting allocfreetrace=1 causes every allocation to be profiled and a stack trace printed on each object's allocation and free. clobberfree: setting clobberfree=1 causes the garbage collector to clobber the memory content of an object with bad content when it frees the object. cgocheck: setting cgocheck=0 disables all checks for packages using cgo to incorrectly pass Go pointers to non-Go code. Setting cgocheck=1 (the default) enables relatively cheap checks that may miss some errors. Setting cgocheck=2 enables expensive checks that should not miss any errors, but will cause your program to run slower. efence: setting efence=1 causes the allocator to run in a mode where each object is allocated on a unique page and addresses are never recycled. gccheckmark: setting gccheckmark=1 enables verification of the garbage collector's concurrent mark phase by performing a second mark pass while the world is stopped. If the second pass finds a reachable object that was not found by concurrent mark, the garbage collector will panic. gcpacertrace: setting gcpacertrace=1 causes the garbage collector to print information about the internal state of the concurrent pacer. gcshrinkstackoff: setting gcshrinkstackoff=1 disables moving goroutines onto smaller stacks. In this mode, a goroutine's stack can only grow. gcstoptheworld: setting gcstoptheworld=1 disables concurrent garbage collection, making every garbage collection a stop-the-world event. Setting gcstoptheworld=2 also disables concurrent sweeping after the garbage collection finishes. gctrace: setting gctrace=1 causes the garbage collector to emit a single line to standard error at each collection, summarizing the amount of memory collected and the length of the pause. The format of this line is subject to change. Currently, it is: gc # @#s #%: #+#+# ms clock, #+#/#/#+# ms cpu, #->#-># MB, # MB goal, # P where the fields are as follows: gc # the GC number, incremented at each GC @#s time in seconds since program start #% percentage of time spent in GC since program start #+...+# wall-clock/CPU times for the phases of the GC #->#-># MB heap size at GC start, at GC end, and live heap # MB goal goal heap size # P number of processors used The phases are stop-the-world (STW) sweep termination, concurrent mark and scan, and STW mark termination. The CPU times for mark/scan are broken down in to assist time (GC performed in line with allocation), background GC time, and idle GC time. If the line ends with "(forced)", this GC was forced by a runtime.GC() call. harddecommit: setting harddecommit=1 causes memory that is returned to the OS to also have protections removed on it. This is the only mode of operation on Windows, but is helpful in debugging scavenger-related issues on other platforms. Currently, only supported on Linux. inittrace: setting inittrace=1 causes the runtime to emit a single line to standard error for each package with init work, summarizing the execution time and memory allocation. No information is printed for inits executed as part of plugin loading and for packages without both user defined and compiler generated init work. The format of this line is subject to change. Currently, it is: init # @#ms, # ms clock, # bytes, # allocs where the fields are as follows: init # the package name @# ms time in milliseconds when the init started since program start # clock wall-clock time for package initialization work # bytes memory allocated on the heap # allocs number of heap allocations madvdontneed: setting madvdontneed=0 will use MADV_FREE instead of MADV_DONTNEED on Linux when returning memory to the kernel. This is more efficient, but means RSS numbers will drop only when the OS is under memory pressure. memprofilerate: setting memprofilerate=X will update the value of runtime.MemProfileRate. When set to 0 memory profiling is disabled. Refer to the description of MemProfileRate for the default value. invalidptr: invalidptr=1 (the default) causes the garbage collector and stack copier to crash the program if an invalid pointer value (for example, 1) is found in a pointer-typed location. Setting invalidptr=0 disables this check. This should only be used as a temporary workaround to diagnose buggy code. The real fix is to not store integers in pointer-typed locations. sbrk: setting sbrk=1 replaces the memory allocator and garbage collector with a trivial allocator that obtains memory from the operating system and never reclaims any memory. scavtrace: setting scavtrace=1 causes the runtime to emit a single line to standard error, roughly once per GC cycle, summarizing the amount of work done by the scavenger as well as the total amount of memory returned to the operating system and an estimate of physical memory utilization. The format of this line is subject to change, but currently it is: scav # # KiB work, # KiB total, #% util where the fields are as follows: scav # the scavenge cycle number # KiB work the amount of memory returned to the OS since the last line # KiB total the total amount of memory returned to the OS #% util the fraction of all unscavenged memory which is in-use If the line ends with "(forced)", then scavenging was forced by a debug.FreeOSMemory() call. scheddetail: setting schedtrace=X and scheddetail=1 causes the scheduler to emit detailed multiline info every X milliseconds, describing state of the scheduler, processors, threads and goroutines. schedtrace: setting schedtrace=X causes the scheduler to emit a single line to standard error every X milliseconds, summarizing the scheduler state. tracebackancestors: setting tracebackancestors=N extends tracebacks with the stacks at which goroutines were created, where N limits the number of ancestor goroutines to report. This also extends the information returned by runtime.Stack. Ancestor's goroutine IDs will refer to the ID of the goroutine at the time of creation; it's possible for this ID to be reused for another goroutine. Setting N to 0 will report no ancestry information. asyncpreemptoff: asyncpreemptoff=1 disables signal-based asynchronous goroutine preemption. This makes some loops non-preemptible for long periods, which may delay GC and goroutine scheduling. This is useful for debugging GC issues because it also disables the conservative stack scanning used for asynchronously preempted goroutines. The net and net/http packages also refer to debugging variables in GODEBUG. See the documentation for those packages for details. The GOMAXPROCS variable limits the number of operating system threads that can execute user-level Go code simultaneously. There is no limit to the number of threads that can be blocked in system calls on behalf of Go code; those do not count against the GOMAXPROCS limit. This package's GOMAXPROCS function queries and changes the limit. The GORACE variable configures the race detector, for programs built using -race. See https://golang.org/doc/articles/race_detector.html for details. The GOTRACEBACK variable controls the amount of output generated when a Go program fails due to an unrecovered panic or an unexpected runtime condition. By default, a failure prints a stack trace for the current goroutine, eliding functions internal to the run-time system, and then exits with exit code 2. The failure prints stack traces for all goroutines if there is no current goroutine or the failure is internal to the run-time. GOTRACEBACK=none omits the goroutine stack traces entirely. GOTRACEBACK=single (the default) behaves as described above. GOTRACEBACK=all adds stack traces for all user-created goroutines. GOTRACEBACK=system is like ``all'' but adds stack frames for run-time functions and shows goroutines created internally by the run-time. GOTRACEBACK=crash is like ``system'' but crashes in an operating system-specific manner instead of exiting. For example, on Unix systems, the crash raises SIGABRT to trigger a core dump. For historical reasons, the GOTRACEBACK settings 0, 1, and 2 are synonyms for none, all, and system, respectively. The runtime/debug package's SetTraceback function allows increasing the amount of output at run time, but it cannot reduce the amount below that specified by the environment variable. See https://golang.org/pkg/runtime/debug/#SetTraceback. The GOARCH, GOOS, GOPATH, and GOROOT environment variables complete the set of Go environment variables. They influence the building of Go programs (see https://golang.org/cmd/go and https://golang.org/pkg/go/build). GOARCH, GOOS, and GOROOT are recorded at compile time and made available by constants or functions in this package, but they do not influence the execution of the run-time system. */
package runtime import ( ) // Caller reports file and line number information about function invocations on // the calling goroutine's stack. The argument skip is the number of stack frames // to ascend, with 0 identifying the caller of Caller. (For historical reasons the // meaning of skip differs between Caller and Callers.) The return values report the // program counter, file name, and line number within the file of the corresponding // call. The boolean ok is false if it was not possible to recover the information. func ( int) ( uintptr, string, int, bool) { := make([]uintptr, 1) := callers(+1, [:]) if < 1 { return } , := CallersFrames().Next() return .PC, .File, .Line, .PC != 0 } // Callers fills the slice pc with the return program counters of function invocations // on the calling goroutine's stack. The argument skip is the number of stack frames // to skip before recording in pc, with 0 identifying the frame for Callers itself and // 1 identifying the caller of Callers. // It returns the number of entries written to pc. // // To translate these PCs into symbolic information such as function // names and line numbers, use CallersFrames. CallersFrames accounts // for inlined functions and adjusts the return program counters into // call program counters. Iterating over the returned slice of PCs // directly is discouraged, as is using FuncForPC on any of the // returned PCs, since these cannot account for inlining or return // program counter adjustment. func ( int, []uintptr) int { // runtime.callers uses pc.array==nil as a signal // to print a stack trace. Pick off 0-length pc here // so that we don't let a nil pc slice get to it. if len() == 0 { return 0 } return callers(, ) } var defaultGOROOT string // set by cmd/link // GOROOT returns the root of the Go tree. It uses the // GOROOT environment variable, if set at process start, // or else the root used during the Go build. func () string { := gogetenv("GOROOT") if != "" { return } return defaultGOROOT } // buildVersion is the Go tree's version string at build time. // // If any GOEXPERIMENTs are set to non-default values, it will include // "X:<GOEXPERIMENT>". // // This is set by the linker. // // This is accessed by "go version <binary>". var buildVersion string // Version returns the Go tree's version string. // It is either the commit hash and date at the time of the build or, // when possible, a release tag like "go1.3". func () string { return buildVersion } // GOOS is the running program's operating system target: // one of darwin, freebsd, linux, and so on. // To view possible combinations of GOOS and GOARCH, run "go tool dist list". const GOOS string = goos.GOOS // GOARCH is the running program's architecture target: // one of 386, amd64, arm, s390x, and so on. const GOARCH string = goarch.GOARCH