github.com/vieux/docker@v0.6.3-0.20161004191708-e097c2a938c7/pkg/pidfile/pidfile.go (about)

     1  // Package pidfile provides structure and helper functions to create and remove
     2  // PID file. A PID file is usually a file used to store the process ID of a
     3  // running process.
     4  package pidfile
     5  
     6  import (
     7  	"fmt"
     8  	"io/ioutil"
     9  	"os"
    10  	"strconv"
    11  	"strings"
    12  )
    13  
    14  // PIDFile is a file used to store the process ID of a running process.
    15  type PIDFile struct {
    16  	path string
    17  }
    18  
    19  func checkPIDFileAlreadyExists(path string) error {
    20  	if pidByte, err := ioutil.ReadFile(path); err == nil {
    21  		pidString := strings.TrimSpace(string(pidByte))
    22  		if pid, err := strconv.Atoi(pidString); err == nil {
    23  			if processExists(pid) {
    24  				return fmt.Errorf("pid file found, ensure docker is not running or delete %s", path)
    25  			}
    26  		}
    27  	}
    28  	return nil
    29  }
    30  
    31  // New creates a PIDfile using the specified path.
    32  func New(path string) (*PIDFile, error) {
    33  	if err := checkPIDFileAlreadyExists(path); err != nil {
    34  		return nil, err
    35  	}
    36  	if err := ioutil.WriteFile(path, []byte(fmt.Sprintf("%d", os.Getpid())), 0644); err != nil {
    37  		return nil, err
    38  	}
    39  
    40  	return &PIDFile{path: path}, nil
    41  }
    42  
    43  // Remove removes the PIDFile.
    44  func (file PIDFile) Remove() error {
    45  	if err := os.Remove(file.path); err != nil {
    46  		return err
    47  	}
    48  	return nil
    49  }