gosema ipc sysv linux

1 files changed, 143 insertions, 0 deletions

diff --git a/main.go b/main.go
new file mode 100644
index 0000000..4300ae4
--- /dev/null
+++ b/main.go
@@ -0,0 +1,143 @@
+package main
+
+import (
+	"crypto/rand"
+	"encoding/hex"
+	"fmt"
+	"gosema/sysv"
+	"os"
+	"time"
+
+	"golang.org/x/sys/unix"
+)
+
+/*
+
+	an example of ipc sysv with golang - this can be done with newer apis
+	like shm_open(), /dev/shm or mmap() too, sysv is the oldest way to do
+	this, and it's commonly used.
+	author: sina@snix.ir
+
+*/
+
+const (
+	//SHMSEMFLG = 0666 | unix.IPC_CREAT | unix.IPC_EXCL
+	SHMSEMFLG = 0666 | unix.IPC_CREAT // open shm and sem with this flag
+	SEMSHEMID = 0x12                  // shm and sem id
+	NUMSOFSEM = 0x01                  // number of sems
+	SHRDMEMRY = 0x20                  // size of shared memory (32 byte)
+)
+
+const SEM_A = 0x00
+
+func clntOrServ() bool {
+	if os.Args[1] == server {
+		return true
+	}
+	if os.Args[1] != client {
+		usage(os.Args[0])
+	}
+	return false
+}
+
+func main() {
+	defer defexit()
+
+	if len(os.Args) < 2 {
+		usage(os.Args[0])
+	}
+
+	serv := clntOrServ()
+
+	semkey, err := sysv.Ftok(os.DevNull, SEMSHEMID)
+	if err != nil {
+		fatal(err)
+	}
+
+	shmkey, err := sysv.Ftok(os.DevNull, SEMSHEMID)
+	if err != nil {
+		fatal(err)
+	}
+
+	shmidd, err := unix.SysvShmGet(int(shmkey), SHRDMEMRY, SHMSEMFLG)
+	if err != nil {
+		fatal(err)
+	}
+
+	defer unix.SysvShmCtl(shmidd, unix.IPC_RMID, &unix.SysvShmDesc{})
+
+	mem, err := unix.SysvShmAttach(shmidd, 0, 0)
+	if err != nil {
+		fatal(err)
+	}
+
+	defer unix.SysvShmDetach(mem)
+
+	if len(mem) != SHRDMEMRY {
+		fatal(errNotSame)
+	}
+
+	logst("shared memory is now ready to use", SHRDMEMRY)
+
+	sempht, err := sysv.NewSemGet(int(semkey), NUMSOFSEM, SHMSEMFLG)
+	if err != nil {
+		fatal(err)
+	}
+
+	defer sempht.DelSem()
+
+	// set semval to 1, which force client to wait for semaphore
+
+	switch {
+	case serv:
+		if err := sempht.SetVal(SEM_A, 1); err != nil {
+			warng(err)
+		}
+
+		for {
+
+			l, _ := sempht.GetVal(SEM_A) // value of semaphore
+			s, _ := sempht.GetPID(SEM_A) // pid that holds semaphore
+			fmt.Printf("sem locked by process pid: %d, semval: %d\n", s, l)
+
+			// lock sem[0], make semval = semval-1 and if semval is 0 then no one
+			// can lock semaphore any more
+			if err := sempht.Lock(SEM_A); err != nil {
+				warng(err)
+				continue
+			}
+
+			// l, _ = sempht.GetVal(SEM_A)
+			// fmt.Println(l)
+
+			// write some dummy random data to shared mem
+			if err := makeRand(mem); err != nil {
+				warng(err)
+			}
+
+			time.Sleep(time.Second) // every one sec
+			fmt.Println("i just put some random jokes in memory.. yeay")
+			if err := sempht.Unlock(SEM_A); err != nil {
+				warng(err)
+			} //unlock sem[0], make semval = semval+1
+		}
+	}
+
+	for {
+		if err := sempht.Lock(SEM_A); err != nil {
+			warng(err)
+			continue // do not unlock it if you haven't locked it
+		}
+
+		fmt.Printf("data: %s\n", hex.EncodeToString(mem))
+		if err := sempht.Unlock(SEM_A); err != nil {
+			warng(err)
+		}
+	}
+}
+
+func makeRand(b []byte) error {
+	_, err := rand.Read(b)
+	return err
+
+}