Context preservation during thread level speculative execution

A processor comprising:

• an execution unit;
• a plurality of registers for storing values generated by the execution unit;
• a synchronization variable table;
• and
• one or more buffers for storing a speculative state of a thread while the thread is being executed in accordance with a thread level speculative execution technique;
• wherein the processor is configured to perform the following:
• during execution of a thread, executing the first instruction that indicates that the thread is entering into speculative execution, the first instruction including an address of a synchronization variable as an argument of the first function, the synchronization variable representing a first range of shared memory addresses that includes at least one memory address that the thread intends to access during speculative execution, executing the first instruction comprising:
• storing, within the processor, a current state of the thread that exists prior to executing the first instruction;
• creating or updating a first SVT entry in the synchronization variable table, the first SVT entry comprising the address of the synchronization variable, an in-use count, and an SVT handle representing the first SVT entry;
• and
• returning the SVT handle;
• during speculative execution of the thread, maintaining, within the one or more buffers, a speculative state of the thread, the speculative state of the thread including a speculative write buffer that includes an entry for each memory address that the thread accesses during speculative execution, the speculative write buffer including a first buffer entry comprising the SVT handle, a particular memory address within the first range of shared memory addresses that was accessed by the first thread, and a value for the particular memory address;
• detecting that the thread will be preempted during speculative execution;
• and
• writing the speculative state to memory to allow the speculative state to be recreated within the processor when execution of the thread is resumed.

A method for storing a speculative write buffer of a thread when the thread is preempted, the method comprising:

• during execution of a thread, executing a first instruction that indicates that the thread is entering into speculative execution, the first instruction including an address of a synchronization variable as an argument of the first function, the synchronization variable representing a first range of shared memory addresses that includes at least one memory address that the thread intends to access during speculative execution, executing the first instruction comprising:
• storing, within the processor, a current state of the thread that exists prior to executing the first instruction;
• creating or updating a first SVT entry in a synchronization variable table, the first SVT entry comprising the address of the synchronization variable, an in-use count, and
• an SVT handle representing the first SVT entry;
• and
• returning the SVT handle;
• during speculative execution of the thread, maintaining within the processor, a speculative state of the thread, the speculative state of the thread including a speculative write buffer that includes an entry for each memory address that the thread accesses during speculative execution, the speculative write buffer including a first buffer entry comprising the SVT handle, a particular memory address within the first range of shared memory addresses that was accessed by the first thread, and a value for the particular memory address;
• detecting that the thread will be preempted during speculative execution;
• storing the speculative state to allow the speculative state to be recreated within the processor when execution of the thread is resumed;
• resuming execution of the thread by restoring the speculative state;
• executing a second instruction that indicates that the thread is exiting speculative execution, the second instruction including the SVT handle;
• using the SVT handle to access the first SVT entry in the synchronization variable table, the access including decrementing the in-use count;
• after decrementing the in-use count, returning the in-use count;
• determining that the in-use count returned from the execution of the second command indicates that no other threads are still accessing the first range of shared addresses;
• determining whether any data collisions occurred during the speculative execution;
• upon determining that no data collisions occurred, accessing the speculative write buffer to identify any entries which define a value written by the thread to the corresponding memory address during the speculative execution;
• and
• for each identified entry, writing the value in the entry to the corresponding memory address.