Using atomic operations to implement a read-write lock

A system for ensuring thread-safe access to a shared data item, the system comprising:

• a plurality of processing cores;
• a memory coupled to the plurality of processing cores, wherein the memory stores instructions that when executed by one or more of the plurality of processing cores, cause one or more of the plurality of processing cores to:
• maintain locking data comprising i) a first portion indicating whether a write operation is updating a data item or awaiting to update the data item, and ii) a second portion indicating a number of read operations accessing the data item;
• receive a first read operation to read the data item;
• repeatedly perform an atomic conditional increment operation until a first locking condition is satisfied, the atomic conditional increment operation comprising, in a single atomic transaction:
• determine, using the locking data, that the first locking condition is satisfied, representing that no write operations are updating the data item or awaiting to update the data item;
• and
• responsive to the determination that the first locking condition is satisfied:
• increment the second portion of the locking data to reflect the number of read operations reading the data item;
• and
• responsive to the determination that the first locking condition is satisfied, execute the first read operation to read the data item.

A non-transitory computer-readable storage medium comprising instructions that, when executed by a processing device, cause the processing device to perform operations comprising:

• maintain, by the processing device, locking data comprising i) a first portion indicating whether a write operation is updating a data item or awaiting to update the data item, and ii) a second portion indicating a number of read operations accessing the data item;
• receive a first read operation to read the data item;
• repeatedly perform an atomic conditional increment operation until a first locking condition is satisfied, the atomic conditional increment operation comprising, in a single atomic transaction:
• determine, using the locking data, that the first locking condition is satisfied, representing that no write operations are updating the data item or awaiting to update the data item;
• and
• responsive to the determination that the first locking condition is satisfied:
• increment the second portion of the locking data to reflect the number of read operations reading the data item;
• and
• responsive to the determination that the first locking condition is satisfied, execute the first read operation to read the data item.