Data commit

Task/Determine-if-only-one-instance-is-running/Go/determine-if-only-one-instance-is-running-1.go

@@ -0,0 +1,19 @@
+package main
+
+import (
+    "fmt"
+    "net"
+    "time"
+)
+
+const lNet = "tcp"
+const lAddr = ":12345"
+
+func main() {
+    if _, err := net.Listen(lNet, lAddr); err != nil {
+        fmt.Println("an instance was already running")
+        return
+    }
+    fmt.Println("single instance started")
+    time.Sleep(10 * time.Second)
+}

Task/Determine-if-only-one-instance-is-running/Go/determine-if-only-one-instance-is-running-2.go

@@ -0,0 +1,24 @@
+package main
+
+import (
+    "fmt"
+    "os"
+    "time"
+)
+
+// The path to the lock file should be an absolute path starting from the root.
+// (If you wish to prevent the same program running in different directories,
+// that is.)
+const lfn = "/tmp/rclock"
+
+func main() {
+    lf, err := os.OpenFile(lfn, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0666)
+    if err != nil {
+        fmt.Println("an instance is already running")
+        return
+    }
+    lf.Close()
+    fmt.Println("single instance started")
+    time.Sleep(10 * time.Second)
+    os.Remove(lfn)
+}

Task/Determine-if-only-one-instance-is-running/Go/determine-if-only-one-instance-is-running-3.go

@@ -0,0 +1,49 @@
+package main
+
+import (
+    "fmt"
+    "os"
+    "strconv"
+    "strings"
+    "time"
+)
+
+// The path to the lock file should be an absolute path starting from the root.
+// (If you wish to prevent the same program running in different directories, that is.)
+const lfn = "/tmp/rclock"
+
+func main() {
+    lf, err := os.OpenFile(lfn, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0666)
+    if err == nil {
+        // good
+        // 10 digit pid seems to be a standard for lock files
+        fmt.Fprintf(lf, "%10d", os.Getpid())
+        lf.Close()
+        defer os.Remove(lfn)
+    } else {
+        // problem
+        fmt.Println(err)
+        // dig deeper
+        lf, err = os.Open(lfn)
+        if err != nil {
+            return
+        }
+        defer lf.Close()
+        fmt.Println("inspecting lock file...")
+        b10 := make([]byte, 10)
+        _, err = lf.Read(b10)
+        if err != nil {
+            fmt.Println(err)
+            return
+        }
+        pid, err := strconv.Atoi(strings.TrimSpace(string(b10)))
+        if err != nil {
+            fmt.Println(err)
+            return
+        }
+        fmt.Println("lock file created by pid", pid)
+        return
+    }
+    fmt.Println(os.Getpid(), "running...")
+    time.Sleep(1e10)
+}