Class: ProcessShared::SharedMemory

Inherits:
FFI::Pointer
  • Object
show all
Includes:
WithSelf
Defined in:
lib/process_shared/shared_memory.rb

Overview

Memory block shared across processes.

Direct Known Subclasses

SharedArray

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Methods included from WithSelf

#with_self

Constructor Details

#initialize(type_or_count = 1, count = 1) ⇒ SharedMemory

Returns a new instance of SharedMemory.



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# File 'lib/process_shared/shared_memory.rb', line 25

def initialize(type_or_count = 1, count = 1)
  @type, @count = case type_or_count
                  when Symbol
                    [type_or_count, count]
                  else
                    [:uchar, type_or_count]
                  end

  @type_size = FFI.type_size(@type)
  @size = @type_size * @count

  name = "/ps-shm#{rand(10000)}"
  @fd = RT.shm_open(name,
                    LibC::O_CREAT | LibC::O_RDWR | LibC::O_EXCL,
                    0777)
  RT.shm_unlink(name)
  
  LibC.ftruncate(@fd, @size)
  @pointer = LibC.mmap(nil,
                       @size,
                       LibC::PROT_READ | LibC::PROT_WRITE,
                       LibC::MAP_SHARED,
                       @fd,
                       0).
    slice(0, size) # slice to get FFI::Pointer that knows its size
                   # (and thus does bounds checking)

  @finalize = self.class.make_finalizer(@pointer.address, @size, @fd)
  ObjectSpace.define_finalizer(self, @finalize)

  super(@pointer)
end

Instance Attribute Details

#count ⇒ Object (readonly)

Returns the value of attribute count.



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# File 'lib/process_shared/shared_memory.rb', line 11

def count
  @count
end

#fd ⇒ Object (readonly)

Returns the value of attribute fd.



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# File 'lib/process_shared/shared_memory.rb', line 11

def fd
  @fd
end

#size ⇒ Object (readonly)

Returns the value of attribute size.



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# File 'lib/process_shared/shared_memory.rb', line 11

def size
  @size
end

#type ⇒ Object (readonly)

Returns the value of attribute type.



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# File 'lib/process_shared/shared_memory.rb', line 11

def type
  @type
end

#type_size ⇒ Object (readonly)

Returns the value of attribute type_size.



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# File 'lib/process_shared/shared_memory.rb', line 11

def type_size
  @type_size
end

Class Method Details

.make_finalizer(addr, size, fd) ⇒ Object 



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# File 'lib/process_shared/shared_memory.rb', line 17

def self.make_finalizer(addr, size, fd)
  proc do
    pointer = FFI::Pointer.new(addr)
    LibC.munmap(pointer, size)
    LibC.close(fd)
  end
end

.open(size, &block) ⇒ Object 



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# File 'lib/process_shared/shared_memory.rb', line 13

def self.open(size, &block)
  new(size).with_self(&block)
end

Instance Method Details

#close ⇒ Object 



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# File 'lib/process_shared/shared_memory.rb', line 102

def close
  ObjectSpace.undefine_finalizer(self)
  @finalize.call
end

#get_object(offset) ⇒ Object

Read the serialized object at offset (in bytes) using Marshal.load.

Returns:

  • (Object) 


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# File 'lib/process_shared/shared_memory.rb', line 84

def get_object(offset)
  io = to_shm_io
  io.seek(offset)
  Marshal.load(io)
end

#put_object(offset, obj) ⇒ Object

Write the serialization of obj (using Marshal.dump) to this shared memory object at offset (in bytes).

Raises IndexError if there is insufficient space.



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# File 'lib/process_shared/shared_memory.rb', line 62

def put_object(offset, obj)
  # FIXME: This is a workaround to an issue I'm seeing in
  # 1.8.7-p352 (not tested in other 1.8's).  If I used the code
  # below that works in 1.9, then inside SharedMemoryIO#write, the
  # passed string object is 'terminated' (garbage collected?) and
  # won't respond to any methods...  This way is less efficient
  # since it involves the creation of an intermediate string, but
  # it works in 1.8.7-p352.
  if RUBY_VERSION =~ /^1.8/
    str = Marshal.dump(obj)
    return put_bytes(offset, str, 0, str.size)
  end

  io = SharedMemoryIO.new(self)
  io.seek(offset)
  Marshal.dump(obj, io)
end

#read_object ⇒ Object

Equivalent to obj)

Returns:

  • (Object) 


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# File 'lib/process_shared/shared_memory.rb', line 98

def read_object
  Marshal.load(to_shm_io)
end

#write_object(obj) ⇒ Object

Equivalent to obj)



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# File 'lib/process_shared/shared_memory.rb', line 91

def write_object(obj)
  put_object(0, obj)
end