example_test.go

     1  // Copyright 2017 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  package runtime_test
     6  
     7  import (
     8  	"fmt"
     9  	"os"
    10  	"runtime"
    11  	"strings"
    12  )
    13  
    14  func ExampleFrames() {
    15  	c := func() {
    16  		// Ask runtime.Callers for up to 10 PCs, including runtime.Callers itself.
    17  		pc := make([]uintptr, 10)
    18  		n := runtime.Callers(0, pc)
    19  		if n == 0 {
    20  			// No PCs available. This can happen if the first argument to
    21  			// runtime.Callers is large.
    22  			//
    23  			// Return now to avoid processing the zero Frame that would
    24  			// otherwise be returned by frames.Next below.
    25  			return
    26  		}
    27  
    28  		pc = pc[:n] // pass only valid pcs to runtime.CallersFrames
    29  		frames := runtime.CallersFrames(pc)
    30  
    31  		// Loop to get frames.
    32  		// A fixed number of PCs can expand to an indefinite number of Frames.
    33  		for {
    34  			frame, more := frames.Next()
    35  
    36  			// Canonicalize function name and skip callers of this function
    37  			// for predictable example output.
    38  			// You probably don't need this in your own code.
    39  			function := strings.ReplaceAll(frame.Function, "main.main", "runtime_test.ExampleFrames")
    40  			fmt.Printf("- more:%v | %s\n", more, function)
    41  			if function == "runtime_test.ExampleFrames" {
    42  				break
    43  			}
    44  
    45  			// Check whether there are more frames to process after this one.
    46  			if !more {
    47  				break
    48  			}
    49  		}
    50  	}
    51  
    52  	b := func() { c() }
    53  	a := func() { b() }
    54  
    55  	a()
    56  	// Output:
    57  	// - more:true | runtime.Callers
    58  	// - more:true | runtime_test.ExampleFrames.func1
    59  	// - more:true | runtime_test.ExampleFrames.func2
    60  	// - more:true | runtime_test.ExampleFrames.func3
    61  	// - more:true | runtime_test.ExampleFrames
    62  }
    63  
    64  func ExampleAddCleanup() {
    65  	tempFile, err := os.CreateTemp(os.TempDir(), "file.*")
    66  	if err != nil {
    67  		fmt.Println("failed to create temp file:", err)
    68  		return
    69  	}
    70  
    71  	ch := make(chan struct{})
    72  
    73  	// Attach a cleanup function to the file object.
    74  	runtime.AddCleanup(&tempFile, func(fileName string) {
    75  		if err := os.Remove(fileName); err == nil {
    76  			fmt.Println("temp file has been removed")
    77  		}
    78  		ch <- struct{}{}
    79  	}, tempFile.Name())
    80  
    81  	if err := tempFile.Close(); err != nil {
    82  		fmt.Println("failed to close temp file:", err)
    83  		return
    84  	}
    85  
    86  	// Run the garbage collector to reclaim unreachable objects
    87  	// and enqueue their cleanup functions.
    88  	runtime.GC()
    89  
    90  	// Wait until cleanup function is done.
    91  	<-ch
    92  
    93  	// Output:
    94  	// temp file has been removed
    95  }
    96
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