Abstract: An exception handling system is described herein that provides one or more distinguished classes of software exceptions that are handled differently than other exceptions. The system treats a distinguished exception as a “hard to catch” exception that is not passed to the catch block of program code unless a developer performs extra steps to acknowledge the distinguished nature of the exception and confirm that the program code is prepared to properly handle the exception. Exceptions that fall into this class are typically those that represent conditions from which normal exception handling practices cannot successfully recover, namely exceptions that corrupt application state. Accordingly, the system prevents the developer from catching these classes of exceptions by default unless the developer explicitly requests to have these exceptions delivered to the program code. Thus, the exception handling system encourages correct programming practices by preventing developer error by default.

Abstract: Various technologies and techniques are disclosed for supporting parallel nested transactions in a transactional memory system. Multiple closed nested transactions are created for a single parent transaction, and the closed nested transactions are executed concurrently as parallel nested transactions. Various techniques are used to ensure effects of the parallel nested transactions are hidden from other transactions outside the parent transaction until the parent transaction commits. For example, retry is allowed to work correctly with parallel nested transactions. When a transaction that is a parallel nested transaction or a child transaction of the parallel nested transaction executes a retry, a read set of the transaction is registered for the retry. When a decision is made to propagate the retry past a parallel nested transaction parent of the transaction, keeping the read set registered and making the read set part of a parent read set.

Abstract: Software transactional memory (STM) primitives are provided that allow the results of prior open calls to be used by subsequent open calls either as-is or through another STM primitive that consumes the results of the previous invocation. The STM primitives are configured to ensure that the address of a shadow copy representing a memory location will not changed across a wide range of operations and thereby enable re-use of the shadow copy.

Abstract: A compiler is provided that determines when the use of software transactional memory (STM) primitives may be optimized with respect to a set of collectively dominating STM primitives. The compiler analysis coordinates the use of variables containing possible shadow copy pointers to allow the analysis to be performed for both direct write and buffered write STM systems. The coordination of the variables containing the possible shadow copy pointers ensures that the results of STM primitives are properly reused. The compiler analysis identifies memory accesses where STM primitives may be eliminated, combined, or substituted for lower overhead STM primitives.

Abstract: An error handling system is described herein that provides a facility for controlling the behavior of software when the software violates a contract condition. The system provides configurable runtime behavior that takes place when a contract fails. The error handling system provides an event that a hosting application or other software code can register to handle and that the system invokes upon detecting a contract failure. The application's response to the event determines how the system handles the failure. If the event is unhandled, the system triggers an escalation policy that allows an administrator or application to specify how the system handles contract failures. Thus, the error handling system provides increased control over the handling of contract failures within software code.

Abstract: A dynamic race detection system is provided that detects race conditions in code that executes concurrently in a computer system. The dynamic race detection system uses a modified software transactional memory (STM) system to detect race conditions. A compiler converts portions of the code that are not configured to operate with the STM system into pseudo STM code that operates with the STM system. The dynamic race detection system detects race conditions in response to either a pseudo STM transaction in the pseudo STM code failing to validate when executed or an actual STM transaction failing to validate when executed because of conflict with a concurrent pseudo STM transaction.

Abstract: A software transactional memory (STM) system allows the composition of traditional lock based synchronization with transactions in STM code. The STM system acquires each traditional lock the first time that a corresponding traditional lock acquire is encountered inside a transaction and defers all traditional lock releases until a top level transaction in a transaction nest commits or aborts. The STM system maintains state information associated with traditional lock operations in transactions and uses the state information to eliminate deferred traditional lock operations that are redundant. The STM system integrates with systems that implement garbage collection.

Abstract: A software transactional memory system is provided with overflow handling. The system includes a global version counter with an epoch number and a version number. The system accesses the global version counter prior to and subsequent to memory accesses of transactions to validate read accesses of the transaction. The system includes mechanisms to detect global version number overflow and may allow some or all transactions to execute to completion subsequent to the global version number overflowing. The system also provides publication, privatization, and granular safety properties.

Abstract: Various technologies and techniques are disclosed that provide software transactional protection of managed pointers. A software transactional memory system interacts with and/or includes a compiler. At compile time, the compiler determines that there are one or more reference arguments in one or more code segments being compiled whose source cannot be recovered. The compiler executes a procedure to select one or more appropriate techniques or combinations thereof for communicating the sources of the referenced variables to the called code segments to ensure the referenced variables can be recovered when needed. Some examples of these techniques include a fattened by-ref technique, a static fattening technique, a dynamic ByRefInfo type technique, and others. One or more combinations of these techniques can be used as appropriate.

Abstract: Various technologies and techniques are disclosed for providing type stability techniques to enhance contention management. A reference counting mechanism is provided that enables transactions to safely examine states of other transactions. Contention management is facilitated using the reference counting mechanism. When a conflict is detected between two transactions, owning transaction information is obtained. A reference count of the owning transaction is incremented. The system ensures that the correct transaction was incremented. If the owning transaction is still a conflicting transaction, then a contention management decision is made to determine proper resolution. When the decision is made, the reference count on the owning transaction is decremented by the conflicting transaction. When each transaction completes, the reference counts it holds to itself is decremented. Data structures cannot be deallocated until their reference count is zero.

Abstract: A software transactional memory system is provided that generates and stores compressed transactional locks in a portion of object headers. The software transactional memory system allocates preferred write log memory with a predefined size of memory that corresponds to a number of bits in the compressed transactional locks. The compressed transactional locks identify write log entries in corresponding write logs in the preferred write log memory. If the preferred write log memory becomes full, additional write log memory is allocated for write log entries and subsequent transactional locks are stored uncompressed in an auxiliary memory. A pointer that may be used to locate the uncompressed transactional lock is stored in the header. If an object header with a compressed transactional lock is needed for another use, the compressed transactional lock is uncompressed and stored in the auxiliary memory. A pointer that may be used to locate the uncompressed transactional lock is stored in the header.

Abstract: The efficient use of type descriptors with frozen objects. A frozen object might actually include several type descriptors, a primary type descriptor that is canonical according to a set of canonicalization rules, and an auxiliary type descriptor that is not identical to the primary type descriptor. The auxiliary type descriptor may be used to access the canonical type descriptor. When performing an operation, if the auxiliary type descriptor can be used to perform the operation, then that auxiliary type descriptor may be used. If the canonical type descriptor is to be used to perform the operation, the auxiliary type descriptor is used to gain access to the canonical primary type descriptor. The primary type descriptor is then used to perform the operation.

Abstract: Various technologies and techniques are disclosed for supporting parallel nested transactions in a transactional memory system. Releasing a duplicate write lock for rollback is supported. During rollback processing of a parallel nested transaction, a write log entry is encountered that represents a write lock. If the write lock is a duplicate, a global lock is used to synchronize access to a global versioned write lock map. Optimistic read validation is supported. During validation, if a versioned write lock indicates a sibling conflict, consult information to determine if a parallel nested transaction should be doomed. Write lock acquisition is supported. Upon attempting to acquire a write lock for a parallel nested transaction, a transactional memory word is analyzed to determine if the write lock can be obtained. If the transactional memory word indicates a versioned write lock, retrieve a write log entry pointer from a global versioned write lock map.

Abstract: Various technologies and techniques are disclosed for supporting parallel nested transactions in a transactional memory system. Multiple closed nested transactions are created for a single parent transaction, and the closed nested transactions are executed concurrently as parallel nested transactions. Various techniques are used to ensure effects of the parallel nested transactions are hidden from other transactions outside the parent transaction until the parent transaction commits. For example, versioned write locks are used with parallel nested transactions. When a transactional memory word changes from a write lock to a versioned write lock, an entry is made in a global versioned write lock map to store a pointer to a write log entry that the versioned write lock replaced. When the versioned write lock is encountered during transaction processing, the global versioned write lock map is consulted to translate the versioned write lock to the pointer to the write log entry.

Abstract: Mechanisms that allow frameworks significant flexibility in varying the library of common base classes in a manner that better suits the domain of applications served by the framework. Instead of providing the base class library, the runtime provides a data contract for the data structure of each base class. The frameworks can then define each base class in a custom way so long as the data contract is honored. Thus, for example, the framework may provide custom framework-specific methods and/or properties as is appropriate for the framework. Another framework might define the base classes in a different way.

Abstract: A software transactional memory (STM) system allows the composition of traditional lock based synchronization with transactions in STM code. The STM system acquires each traditional lock the first time that a corresponding traditional lock acquire is encountered inside a transaction and defers all traditional lock releases until a top level transaction in a transaction nest commits or aborts. The STM system maintains state information associated with traditional lock operations in transactions and uses the state information to eliminate deferred traditional lock operations that are redundant. The STM system integrates with systems that implement garbage collection.

Abstract: An exception notification system is described herein that provides an early notification that a software exception has occurred before exception handling code has run. The exception notification system receives a registration request from program code to register a handler to receive an early notification when an exception occurs. When an exception occurs, the system raises an event that calls each registered handler. After the handler returns, the system performs normal exception handling, so that the early notification does not change existing exception-handling behavior. The exception notification system allows a program to inspect and log an exception before the program state has been modified by exception handling. The program code can capture detailed information about the cause of the exception to enable further offline analysis. Thus, the exception notification system allows developers to improve their programs by receiving more information about unexpected conditions in the program code.

Abstract: Various technologies and techniques are disclosed for providing type stability techniques to enhance contention management. A reference counting mechanism is provided that enables transactions to safely examine states of other transactions. Contention management is facilitated using the reference counting mechanism. When a conflict is detected between two transactions, owning transaction information is obtained. A reference count of the owning transaction is incremented. The system ensures that the correct transaction was incremented. If the owning transaction is still a conflicting transaction, then a contention management decision is made to determine proper resolution. When the decision is made, the reference count on the owning transaction is decremented by the conflicting transaction. When each transaction completes, the reference counts it holds to itself is decremented. Data structures cannot be deallocated until their reference count is zero.

Abstract: Various technologies and techniques are disclosed for providing type stability techniques to enhance contention management. A reference counting mechanism is provided that enables transactions to safely examine states of other transactions. Contention management is facilitated using the reference counting mechanism. When a conflict is detected between two transactions, owning transaction information is obtained. A reference count of the owning transaction is incremented. The system ensures that the correct transaction was incremented. If the owning transaction is still a conflicting transaction, then a contention management decision is made to determine proper resolution. When the decision is made, the reference count on the owning transaction is decremented by the conflicting transaction. When each transaction completes, the reference counts it holds to itself is decremented. Data structures cannot be deallocated until their reference count is zero.

Abstract: Various technologies and techniques are disclosed for supporting parallel nested transactions in a transactional memory system. For example, pessimistic reads are supported. A pessimistic duplication detection data structure is created for a parallel nested transaction. An entry is made into the data structure for each pessimistic read in the parallel nested transaction. When committing the parallel nested transaction, new pessimistic read locks are passed to an immediate parent, and an entry is made into a separate pessimistic duplication detection data structure of the immediate parent with synchronization between sibling transactions. The pessimistic duplication detection data structures can also be used for upgrades from pessimistic reads to write locks. Retry operations are supported with parallel nested transactions. Write abort compensation maps can be used with parallel nested transactions to detect and handle falsely doomed parent transactions.