SemaphoreLocker Class Reference

Handles creation, locking and unlocking of System V semaphores. More...

#include <SemaphoreLocker.h>

Public Member Functions
	SemaphoreLocker (int semId)
	Lock the given semaphore.
	~SemaphoreLocker ()
	Unlock.
void	lock ()
	Lock the semaphore.
void	unlock ()
	Unlock the semaphore.

Static Public Member Functions
static int	create (key_t semkey)
	Create a new semaphore and initialize it.
static void	destroy (int semId)
	Destroy the given semaphore.
static bool	isLocked (int semId)
	Return true if the given semaphore is locked.

Private Attributes
int	m_id
	semaphore id, see semget(2).

Detailed Description

Handles creation, locking and unlocking of System V semaphores.

create() is used to create a new semaphore with a given semaphore key.

The returned semaphore id can then be used to protect critical sections by constructing an instance of this class. The semaphore is unlocked again on destruction.

Definition at line 24 of file SemaphoreLocker.h.

Constructor & Destructor Documentation

SemaphoreLocker()

SemaphoreLocker ( int  semId )

inlineexplicit

Lock the given semaphore.

Definition at line 27 of file SemaphoreLocker.h.

: m_id(semId) { lock(); }

~SemaphoreLocker()

~SemaphoreLocker ( )

inline

Unlock.

Definition at line 29 of file SemaphoreLocker.h.

{ unlock(); }

Member Function Documentation

create()

int create ( key_t  semkey )

static

Create a new semaphore and initialize it.

Returns the semaphore id or value < 0 on error.

Definition at line 19 of file SemaphoreLocker.cc.

{
  int semid = semget(semkey, 1, IPC_CREAT | IPC_EXCL | 0600);
  if (semid >= 0) {
    // POSIX doesn't guarantee any particular state of our fresh semaphore
    int semval = 1; //unlocked state
    if (semctl(semid, 0, SETVAL, semval) == -1) { //set 0th semaphore to semval
      B2ERROR("Initializing semaphore with semctl() failed.");
    }
  } else if (errno == EEXIST) {
    semid = semget(semkey, 1, 0600);
  }
  if (semid < 0) {
    B2ERROR("Couldn't create semaphore with semget()! Maybe you have too many semaphores from aborted processes lying around, you can clean those up by running 'clear_basf2_ipc'.");
    return semid;
  }
 
  return semid;
}

destroy()

void destroy ( int  semId )

static

Destroy the given semaphore.

Definition at line 39 of file SemaphoreLocker.cc.

{
  if (semctl(semId, 1, IPC_RMID) == -1) { //semnum=1 has no meaning, ignored
    B2ERROR("Error in SemaphoreLocker::destroy(), semaphore " << semId << ", error: " << strerror(errno));
  }
}

isLocked()

bool isLocked ( int  semId )

static

Return true if the given semaphore is locked.

If you know the lock might be held by the current process (e.g. while in a signal handler), locking is only safe if this returns false.

Definition at line 46 of file SemaphoreLocker.cc.

{
  int ignored = 0;
  int val = semctl(semId, 0, GETVAL, ignored);
  return (val == 0); //0: locked, 1: unlocked
 
}

lock()

void lock

(

)

Lock the semaphore.

If the semaphore is locked, this function will block until it can acquire a lock.

Definition at line 72 of file SemaphoreLocker.cc.

{
  doSemOp(m_id, -1);
}

unlock()

void unlock

(

)

Unlock the semaphore.

Definition at line 77 of file SemaphoreLocker.cc.

{
  doSemOp(m_id, 1);
}

Member Data Documentation

m_id

int m_id

private

semaphore id, see semget(2).

Definition at line 52 of file SemaphoreLocker.h.

---

The documentation for this class was generated from the following files:

• framework/pcore/include/SemaphoreLocker.h
• framework/pcore/src/SemaphoreLocker.cc