Class: Ferret::Store::Lock

### Home Classes Methods

### In Files

- ext/r_store.c

### Parent

Object

### Namespace

- CLASS Ferret::Store::Lock::LockError

### Methods

- #locked?
- #obtain
- #release
- #while_locked

### Files

- MIT-LICENSE
- README
- TODO
- TUTORIAL

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# Ferret::Store::Lock

A Lock is used to lock a data source so that not more than one output stream can access a data source at one time. It is possible that locks could be disabled. For example a read only index stored on a CDROM would have no need for a lock.

You can use a lock in two ways. Firstly:

    write_lock = @directory.make_lock(LOCK_NAME)
    write_lock.obtain(WRITE_LOCK_TIME_OUT)
      ... # Do your file modifications # ...
    write_lock.release()

Alternatively you could use the while locked method. This ensures that the lock will be released once processing has finished.

    write_lock = @directory.make_lock(LOCK_NAME)
    write_lock.while_locked(WRITE_LOCK_TIME_OUT) do
      ... # Do your file modifications # ...
    end

### Public Instance Methods

locked? → bool click to toggle source

Returns true if the lock has been obtained.

    static VALUE
    frb_lock_is_locked(VALUE self)
    {
        Lock *lock;
        GET_LOCK(lock, self);
        return lock->is_locked(lock) ? Qtrue : Qfalse;
    }

obtain(timeout = 1) → bool click to toggle source

Obtain a lock. Returns true if lock was successfully obtained. Make sure the lock is released using Lock#release. Otherwise you'll be left with a stale lock file.

The timeout defaults to 1 second and 5 attempts are made to obtain the lock. If you're doing large batch updates on the index with multiple processes you may need to increase the lock timeout but 1 second will be substantial in most cases.

timeout | seconds to wait to obtain lock before timing out and returning false
return | true if lock was successfully obtained. Raises a Lock::LockError otherwise.

    static VALUE
    frb_lock_obtain(int argc, VALUE *argv, VALUE self)
    {
        VALUE rtimeout;
        int timeout = 1;
        Lock *lock;
        GET_LOCK(lock, self);

        if (rb_scan_args(argc, argv, "01", &rtimeout) > 0) {
            timeout = FIX2INT(rtimeout);
        }
        /* TODO: use the lock timeout */
        if (!lock->obtain(lock)) {
            rb_raise(cLockError, "could not obtain lock: #%s", lock->name);
        }
        return Qtrue;
    }

release() → self click to toggle source

Release the lock. This should only be called by the process which obtains the lock.

    static VALUE
    frb_lock_release(VALUE self)
    {
        Lock *lock;
        GET_LOCK(lock, self);
        lock->release(lock);
        return self;
    }

while_locked(timeout = 1) { do_something() } → bool click to toggle source

Run the code in a block while a lock is obtained, automatically releasing the lock when the block returns.

See Lock#obtain for more information on lock timeout.

timeout | seconds to wait to obtain lock before timing out and returning false
return | true if lock was successfully obtained. Raises a Lock::LockError otherwise.

    static VALUE
    frb_lock_while_locked(int argc, VALUE *argv, VALUE self)
    {
        VALUE rtimeout;
        int timeout = 1;
        Lock *lock;
        GET_LOCK(lock, self);
        if (rb_scan_args(argc, argv, "01", &rtimeout) > 0) {
            timeout = FIX2INT(rtimeout);
        }
        if (!lock->obtain(lock)) {
            rb_raise(cLockError, "could not obtain lock: #%s", lock->name);
        }
        rb_yield(Qnil);
        lock->release(lock);
        return Qtrue;
    }

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