Reactive programming subscription context

A computer-implemented method comprising:

• receiving, by a reactive programming system comprising one or more computers, a reactive programming program defining an ordering of a plurality of operators, the plurality of operators including a subscriber context operator that writes a value to a subscription context for a particular subscriber, wherein the ordering defines an upstream subscription flow ordering from the particular subscriber to a publisher and a downstream data flow ordering from the publisher to the particular subscriber, and wherein the value written to the subscription context is only available to operators that are upstream from the subscriber context operator, and wherein the plurality of operators include a second subscriber context operator that is upstream from the subscriber context operator, and wherein updating the subscription context for the second subscriber context operator comprises merging a second value written by the second subscriber context with the value written by the subscriber context operator;
• evaluating, by the reactive programming system, the operators in the upstream subscription flow ordering, including updating a subscription context of each operator with the value written by the subscriber context operator;
• and
• upon receiving an input data item, processing, by the reactive programming system, the input data item using the operators in the downstream data flow ordering to generate a final output data item for the input data item, wherein one or more operators that are executed in the downstream data flow ordering access the value of the subscription context written by the subscriber context operator during evaluation of the operations in the upstream subscription flow ordering regardless of which threads executed the respective operators.

A computer program product, encoded on one or more non-transitory computer storage media, comprising instructions that when executed by one or more computers of a reactive programming system cause the one or more computers to perform operations comprising:

• receiving a reactive programming program defining an ordering of a plurality of operators, the plurality of operators including a subscriber context operator that writes a value to a subscription context for a particular subscriber, wherein the ordering defines an upstream subscription flow ordering from the particular subscriber to a publisher and a downstream data flow ordering from the publisher to the particular subscriber, and wherein the value written to the subscription context is only available to operators that are upstream from the subscriber context operator, and wherein the plurality of operators include a second subscriber context operator that is upstream from the subscriber context operator, and wherein updating the subscription context for the second subscriber context operator comprises merging a second value written by the second subscriber context with the value written by the subscriber context operator;
• evaluating the operators in the upstream subscription flow ordering, including updating a subscription context of each operator with the value written by the subscriber context operator;
• and
• upon receiving an input data item, processing the input data item using the operators in the downstream data flow ordering to generate a final output data item for the input data item, wherein one or more operators that are executed in the downstream data flow ordering access the value of the subscription context written by the subscriber context operator during evaluation of the operations in the upstream subscription flow ordering regardless of which threads executed the respective operators.