Semi-blocking deterministic directory coherence

A method comprising:

• receiving a first request for a requested coherence unit from a first requesting node, and the first request identifies the requested coherence unit and requests that a specified coherency state for the requested coherence unit be provided to the first requesting node, and the requested coherence unit has a corresponding entry in a coherence directory, wherein the corresponding entry stores a state identifying which nodes in a multi-node computer system are storing a copy of the coherence unit and further identifying a coherence state of the coherence unit according to a coherence protocol implemented in the computer system;
• receiving a second request for the requested coherence unit prior to completing coherence activity for the first request, the second request from a second requesting node, and the second request identifies the requested coherence unit and requests that a specified coherency state for the requested coherence unit be provided to the second requesting node;
• and
• selectively initiating coherence activity for the second request, prior to a completion of coherence activity for the first request, dependent on a type of the second request.

A system comprising:

• a first node configured to transmit a first request for a requested coherence unit, the first request identifying the requested coherence unit and requesting that a specified coherency state for the requested coherence unit be provided to the first node;
• a second node configured to transmit a second request for the requested coherence unit, the second request identifying the requested coherence unit and requesting that a specified coherency state for the requested coherence unit be provided to the second node;
• and
• a third node coupled to the first node and the second node, wherein the third node comprises a coherence directory comprising a plurality of entries, wherein each entry corresponds to a respective coherence unit and stores a state identifying which nodes in the system are storing a copy of the coherence unit and further identifying a coherence state of the coherence unit according to a coherence protocol implemented in the system, and wherein the third node is configured to initiate coherence activity for the first request, and wherein the third node is configured to selectively initiate coherence activity for the second request, prior to a completion of coherence activity for the first request, dependent on a type of the second request.