Composite lock for computer systems with multiple domains

In a computer system that has a hardware platform, a software platform, a resource and a plurality of user-defined domains, a lock for controlling access to the resource by a plurality of processes, the lock comprising:

• A) a platform-dependent lock component that operates as a semaphore with a wait function and a signal function;
• B) a front-end lock component comprising computer instructions
• i) for acquiring the lock and granting access to the resource by performing a fetch-and-increment operation on a variable, which indicates how many of the processes currently hold or wish to acquire the lock,
• a) by atomically changing the variable by a first predetermined amount as part of the first operation;
• and
• b) by calling the wait function of the platform-dependent lock component if the variable meets a first comparison condition relative to a predetermined first threshold value,
• ii) for releasing the lock by performing a fetch-and-decrement operation on the variable
• a) by atomically changing the variable by a second predetermined amount as part of the second operation;
• and
• b) by calling the signal function of the platform-dependent lock component if the variable meets a second comparison condition relative to a predetermined second threshold value;
• C) the processes calling the front-end lock component in order to acquire the lock and access the resource regardless of the current domain in which each process is currently executing;
• D) the platform-dependent lock component and the front-end lock component being accessible from different domains;
• E) only one of the processes at a time thereby being allowed to hold the lock;
• in which:
• F) the first comparison condition is that the variable indicates that at least one of the processes currently holds or wishes to acquire the lock;
• and
• G) the second comparison condition is that the variable indicates that at least one of the processes wishes to acquire the lock in addition to the process that currently holds the lock.

A computer system comprising:

• a host hardware platform;
• host software that includes a platform-provided lock component;
• a virtual machine (VM);
• a virtual machine monitor that forms a software interface between the VM and the host hardware platform;
• a plurality of user-defined domains including a host domain and a VM domain;
• a composite lock that has a front-end component that is accessible to processes running in both the host domain and the VM domain and that conditionally calls the platform-provided lock component in the case of contention for the composite lock.

In a computer system that has a hardware platform, a software platform and a plurality of user-defined domains, a method for controlling concurrently running processes comprising:

• A) running as a semaphore a platform-dependent lock component with a wait function and a signal function;
• B) running a front-end lock component to include the following sub-steps:
• i) acquiring the lock by performing a first operation on a variable, which indicates how many of the processes currently hold or wish to acquire the lock,
• a) by atomically changing the variable by a first predetermined amount as part of the first operation;
• and
• b) by calling the wait function of the platform-dependent lock component if the variable meets a first comparison condition relative to a predetermined first threshold value,
• ii) releasing the lock by performing a second operation on the variable
• a) by atomically changing the variable by a second predetermined amount as part of the second operation;
• and
• b) by calling the signal function of the platform-dependent lock component if the variable meets a second comparison condition relative to a predetermined second threshold value;
• C) processes calling the front-end lock component in order to access the resource regardless of the current domain in which each process is currently executing;
• D) the platform-dependent lock component and the front-end lock component being accessible from different domains;
• E) thereby allowing only one of the processes at a time to acquire the lock.

In a computer system that has a hardware platform, a software platform and a plurality of user-defined domains, a method for controlling concurrently running processes comprising:

• A) running as a semaphore a platform-dependent lock component with a wait function and a signal function;
• B) running a front-end lock component to include the following sub-steps:
• i) acquiring the lock by performing a fetch-and-increment operation on a variable, which indicates how many of the processes currently hold or wish to acquire the lock,
• a) by atomically changing the variable by a first predetermined amount as part of the first operation;
• and
• b) by calling the wait function of the platform-dependent lock component if the variable meets a first comparison condition relative to a predetermined first threshold value, in which the first comparison condition is that the variable indicates that at least one of the processes currently holds or wishes to acquire the lock;
• ii) releasing the lock by performing a fetch-and-decrement operation on the variable
• a) by atomically changing the variable by a second predetermined amount as part of the second operation;
• and
• b) by calling the signal function of the platform-dependent lock component if the variable meets a second comparison condition relative to a predetermined second threshold value, in which the second comparison condition is that the variable indicates that at least one of the processes wishes to acquire the lock in addition to the process that currently holds the lock;
• C) processes calling the front-end lock component in order to access the resource regardless of the current domain in which each process is currently executing;
• D) the platform-dependent lock component and the front-end lock component being accessible from different domains;
• E) thereby allowing only one of the processes at a time to acquire the lock.