| 1 | /** |
| 2 | * Copyright (c) Meta Platforms, Inc. and affiliates. |
| 3 | * |
| 4 | * This source code is licensed under the MIT license found in the |
| 5 | * LICENSE file in the root directory of this source tree. |
| 6 | * |
| 7 | * @flow |
| 8 | */ |
| 9 | |
| 10 | import {REACT_CONSUMER_TYPE, REACT_CONTEXT_TYPE} from 'shared/ReactSymbols'; |
| 11 | |
| 12 | import type {ReactContext} from 'shared/ReactTypes'; |
| 13 | |
| 14 | export function createContext<T>(defaultValue: T): ReactContext<T> { |
| 15 | // TODO: Second argument used to be an optional `calculateChangedBits` |
| 16 | // function. Warn to reserve for future use? |
| 17 | |
| 18 | const context: ReactContext<T> = { |
| 19 | $$typeof: REACT_CONTEXT_TYPE, |
| 20 | // As a workaround to support multiple concurrent renderers, we categorize |
| 21 | // some renderers as primary and others as secondary. We only expect |
| 22 | // there to be two concurrent renderers at most: React Native (primary) and |
| 23 | // Fabric (secondary); React DOM (primary) and React ART (secondary). |
| 24 | // Secondary renderers store their context values on separate fields. |
| 25 | _currentValue: defaultValue, |
| 26 | _currentValue2: defaultValue, |
| 27 | // Used to track how many concurrent renderers this context currently |
| 28 | // supports within in a single renderer. Such as parallel server rendering. |
| 29 | _threadCount: 0, |
| 30 | // These are circular |
| 31 | Provider: null as any, |
| 32 | Consumer: null as any, |
| 33 | }; |
| 34 | |
| 35 | context.Provider = context; |
| 36 | context.Consumer = { |
| 37 | $$typeof: REACT_CONSUMER_TYPE, |
| 38 | _context: context, |
| 39 | }; |
| 40 | if (__DEV__) { |
| 41 | context._currentRenderer = null; |
| 42 | context._currentRenderer2 = null; |
| 43 | } |
| 44 | |
| 45 | return context; |
| 46 | } |