Method and apparatus for preventing deadlock in a distributed shared memory system

An apparatus for preventing a deadlock in a distributed shared memory system having a memory access request transaction queue having a plurality of queue slots, comprising:

• a coherency controller configured to prevent a blocking flow control class transaction from being stored in at least one of said plurality of queue slots;
• said coherency controller is configured to store a processor return flow control class transaction in said at least one of said plurality of queue slots;
• a first register configured to store a blocking flow control class transaction threshold indicating a maximum number of blocking flow control class transactions allowed to be processed in said memory access request transaction queue;
• and
• wherein said coherency controller is configured to prevent said memory access request transaction queue from accepting any new blocking flow control class transaction if a current number of blocking flow control class transactions already in said memory access request transaction queue is not less than said blocking flow control class transaction threshold.

A method of providing a distributed memory return transaction queue in a distributed shared memory system having a memory access request transaction queue processing one or more entries, comprising:

• providing each of said one or more entries a plurality of addition lines;
• providing a global pointer that indicates a last occupied position in said distributed memory return transaction queue;
• providing a plurality of entry pointers each associated with said one or more entries;
• and
• allowing each of said one or more entries to add one or more memory return transaction at locations in said distributed memory return transaction queue based on said global pointer and associated ones of said plurality of entry pointers through said a plurality of addition lines during a clock cycle.