PyArrow Plasma object ids, "sealing" makes an object immutable, pyristent

https://arrow.apache.org/docs/python/plasma.html#object-ids
https://arrow.apache.org/docs/python/plasma.html#creating-an-object-buffer

> Objects are created in Plasma in two stages. First, they are created, which allocates a buffer for the object. At this point, the client can write to the buffer and construct the object within the allocated buffer.
>
> To create an object for Plasma, you need to create an object ID, as well as give the object’s maximum size in bytes.
> ```python
> # Create an object buffer.
> object_id = plasma.ObjectID(20 * b"a")
> object_size = 1000
> buffer = memoryview(client.create(object_id, object_size))
>
> # Write to the buffer.
> for i in range(1000):
>   buffer[i] = i % 128
> ```
>
> When the client is done, the client seals the buffer, making the object immutable, and making it available to other Plasma clients.
>
> ```python
> # Seal the object. This makes the object immutable and available to other clients.
> client.seal(object_id)
> ```

https://pypi.org/project/pyrsistent/ also supports immutable structures

On Sat, Aug 1, 2020 at 4:44 PM Eric V. Smith <eric@trueblade.com> wrote:
On 8/1/2020 1:25 PM, Marco Sulla wrote:
> You don't need locks with immutable objects. Since they're immutable,
> any operation that usually will mutate the object, generate another
> immutable instead. The most common example is str: the sum of two
> strings in Python (and in many other languages) produces a new string.

While they're immutable at the Python level, strings (and all other
objects) are mutated at the C level, due to reference count updates. You
need to consider this if you're sharing objects without locking or other
synchronization.

Eric

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