US 7,584,463 B2Granted

State as a first-class citizen of an imperative language

AssigneeMicrosoft Corporation

InventorsWolfgang Grieskamp, Yuri Gurevich, Wolfram Schulte, Nikolai Tillmann

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Abstract

A state component saves a present state of a program or model. This state component can be invoked by the program or model itself, thereby making state a first-class citizen. As the state of the program evolves from the saved state, the saved state remains for reflection and recall, for example, for testing, verification, transaction processing, etc. Using a state reference token, the saved state of the program or model can be accessed by the program or model. For example, the program or model by utilizing a state component, can return itself to the saved state. After returning to the saved state, a second execution path can be introduced without requiring re-execution of the actions leading to the saved state. In another example, the state space of an executing model is saved in order to generate inputs required to exercise a program or model.

Claims17

Dependent claims

A computer readable storage medium having stored thereon a data structure for saving state of an executing program a plurality of times as the executing program executes over time, the data structure comprising:

a first state frame comprising a representation of a first state of the executing program;
a second state frame comprising a representation of a second state of the executing program comprising state changes made by the executing program after the first state frame is created and the second state frame includes a pointer back to the first state frame;
and
a third state frame comprising a representation of state changes made by the executing program after a fork method creates the third state frame, and the third state frame includes a pointer back to the second state frame;
wherein the representations of state form a chain of state frames;
wherein a first state of the executing program is saved in the first state frame as a semantically accessible first state object, and a second state of the executing program is saved in the second state frame as a semantically accessible second state object;
wherein the third state frame is empty when created by the fork method;
wherein, after the fork method creates the third state frame, a value of a variable of the executing program can be accessed by checking, in backwards order that the state frames were created, for the value of the variable in the chain of state frames;
and
wherein at least one of the state frames in the chain of state frames comprises a cached value copied from a prior frame in the chain of state frames.

7 more elements

A computerized method comprising:

via an application programming interface, receiving a request to create a state save;
in response to the request, at a first point in time, saving, by a computer, a first representation of a state of an executing program, wherein the saving comprises copying state of the executing program at the first point in time to a first state frame;
creating a blank state frame with a backward link to the first state frame as a first current state frame;
in the first current state frame, maintaining a representation of subsequent state comprising changes made to the state of the executing program after the first point in time;
via the application programming interface, receiving an other request to create a state save;
in response to the other request, at a second point in time, saving the first current state frame as a second state frame with a backward pointer to the first state frame;
creating an other blank state frame with a backward link to the second state frame as a subsequent current state frame, whereby a chain of state frames is generated;
in the subsequent current state frame, maintaining a representation of subsequent state comprising changes made to the state of the executing program after the second point in time;
in response to a request for a value of a variable after the request to create a state save, checking for the value of the variable, wherein the checking comprises walking backward through the chain of state frames from a last state frame toward the first state frame until an update to the value for the variable in the chain of state frames is found;
in response to the request for the value of the variable, returning the update to the value for the variable in the chain of state frames as the value of the variable;
and
as a result of the request for the value of the variable, copying an update from a prior state frame to a current state frame, thereby speeding up further accesses to the variable.

9 more elements

One or more computer-readable storage media having stored thereon computer-executable instructions for performing a method comprising:

receiving a request to create a state save;
in response to the request, at a first point in time, saving a first representation of a state of an executing program, wherein the saving comprises copying state of the executing program at the first point in time to a first state frame;
creating a blank state frame with a backward link to the first state frame as a first current state frame;
in the first current state frame, maintaining a representation of subsequent state comprising changes made to the state of the executing program after the first point in time;
receiving an other request to create a state save;
in response to the other request, at a second point in time, saving the first current state frame as a second state frame with a backward pointer to the first state frame;
creating an other blank state frame with a backward link to the second state frame as a subsequent current state frame, whereby a chain of state frames is generated;
in the subsequent current state frame, maintaining a representation of subsequent state comprising changes made to the state of the executing program after the second point in time;
in response to a request for a value of a variable after the request to create a state save, checking for the value of the variable, wherein the checking comprises walking backward through the chain of state frames from a last state frame toward the first state frame until an update to the value for the variable in the chain of state frames is found;
as the value of the variable, returning the update to the value for the variable in the chain of state frames;
and
as a result of the request for the value of the variable, copying an update from a prior state frame to a current state frame, thereby speeding up further accesses to the variable.

9 more elements

A specialized computer apparatus comprising:

a processor;
memory readable by the processor and storing computer-executable instructions for performing a method comprising:
receiving a request to create a state save;
in response to the request, at a first point in time, saving a first representation of a state of an executing program, wherein the saving comprises copying state of the executing program at the first point in time to a first state frame;
creating a blank state frame with a backward link to the first state frame as a first current state frame;
in the first current state frame, maintaining a representation of subsequent state comprising changes made to the state of the executing program after the first point in time;
receiving an other request to create a state save;
in response to the other request, at a second point in time, saving the first current state frame as a second state frame with a backward pointer to the first state frame;
creating an other blank state frame with a backward link to the second state frame as a subsequent current state frame, whereby a chain of state frames is generated;
in the subsequent current state frame, maintaining a representation of subsequent state comprising changes made to the state of the executing program after the second point in time;
in response to a request for a value of a variable after the request to create a state save, checking for the value of the variable, wherein the checking comprises walking backward through the chain of state frames from a last state frame toward the first state frame until an update to the value for the variable in the chain of state frames is found;
as the value of the variable, returning the update to the value for the variable in the chain of state frames;
and
as a result of the request for the value of the variable, copying an update from a prior state frame to a current state frame, thereby speeding up further accesses to the variable;
wherein at least one state frame in the chain of state frames comprises a timestamp.

12 more elements

Dependencies are inferred from the claim text.