Electrical computers and digital data processing systems: input/ – Access locking
Reexamination Certificate
1998-12-03
2001-05-08
Etienne, Ario (Department: 2155)
Electrical computers and digital data processing systems: input/
Access locking
C710S240000, C711S152000
Reexamination Certificate
active
06230230
ABSTRACT:
FIELD OF THE PRESENT INVENTION
The present invention relates to microprocessors, and more particularly, to locking of computer resources.
BACKGROUND
When different computer entities such as computer processes or threads share a computer resource (for example, data, code, or a piece of hardware), it may be desirable to allow one of the computer entities to lock a resource for a while to prevent some types of access to the resource by other computer entities. For example, if two or more threads share computer data, and one thread has started but not finished to modify the data when another thread is accessing the data, the other thread may get incorrect information from the data and/or the data could be corrupted by the two threads. Also, if one thread has started but not finished execution of a critical code section when another thread starts executing the same code section, execution errors may occur if, for example, the critical code section modifies the state of a data area, a hardware controller, or some other computer resource. Therefore, locking techniques have been provided to allow computer entities to lock computer resources.
It is desirable to provide fast techniques for locking of computer resources.
SUMMARY
The present invention provides elimination of traps and atomics in thread synchronization. Efficient and fast thread synchronization is provided. For example, thread synchronization can be efficient and fast in some frequently occurring situations, such as when a thread owns a computer resource (e.g., has a lock on a computer resource).
In one embodiment, a lock cache (e.g., four registers) that holds up to four values, each of which is a reference to a locked object (e.g., an address of the locked object) is provided. The lock cache maintains LOCKCOUNTs. A lockcachecheck instruction (e.g., lockcachecheck object_address, Rd) returns a first predetermined value if the object_address is stored in the lock_cache (e.g., the current thread executing on the processor owns the object). Otherwise, the lockcachecheck instruction returns a second predetermined value (e.g., the lock cache is not currently storing the object_address, and the current thread may or may not own the object, which can be determined based on an access to memory that is handled in software). For example, if the first predetermined value is returned, then processing can continue with the current instruction stream (the current thread owns the object). If the second predetermined value is returned, then processing can branch to a different set of instructions (e.g., to check a table in memory to determine whether the current thread owns the object, and if not, then the current thread can wait for the object to become available).
Other features and advantages of the present invention are described below.
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Joy William N.
O'Connor James M.
Tremblay Marc
Etienne Ario
Odozynski John A.
Skjerven Morrill & MacPherson LLP
Sun Microsystems Inc.
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