Semaphore library Back

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require('sem')

Include library before calling semaphore functions

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[res1, [res2, [...]]] = sem.runlocked(name, timeout, callback, [param1, [param2, [...]]])

Runs callback function in locked mode, returning all callback results as is. First parameter passed to callback is lock status - true when lock was acquired, false when locking failed, nil when semaphore creation failed.

Parameters:

• name shared semaphore name
• timeout maximum time to wait in seconds for semaphore to become unlocked
• callback function to execute in locked mode
• param1, param2, ... optional additional parameters to pass to callback

Example (event script with locking):

require('sem')

-- wait for 5 seconds max before executing callback
res1, res2 = sem.runlocked('eventlock', 5, function(lockres)
  -- lock acquired
  if lockres then
    return true, 'lock ok'
  -- failed to acquire lock
  else
    return nil, 'lock failed'
  end
end)

log(res1, res2)

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semaphore = sem.open(name, [value = 1])

Opens shared semaphore, returns semaphore handle or generates an error on failure

Parameters:

• name shared semaphore name, required
• value initial value, optional, defaults to 1 (semaphore is unlocked)

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semaphore:getvalue()

Returns the current value of the semaphore or nil on error. Zero value means that the semaphore is locked

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semaphore:post()

Increments (unlocks) the semaphore

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semaphore:trywait()

Checks if the semaphore is locked, returns true and decrements the semaphore when the value is non-zero, false otherwise

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semaphore:wait([timeout])

Decrements the semaphore with optional timeout in seconds.
Warning when no timeout is specified, this function will block until semaphore is incremented.

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semaphore:close()

Closes the semaphore. Not required, semaphore handles are closed automatically when script execution ends