--- title: "Build before starting the emulator" description: "Compile the app first, then boot the emulator and install the finished build." url: https://starsling.dev/ci-playbooks/techniques/avoid-emulator-build-contention canonicalUrl: https://starsling.dev/ci-playbooks/techniques/avoid-emulator-build-contention --- # Build before starting the emulator Compile the app first, then boot the emulator and install the finished build. ## How to choose an approach This technique currently has one documented company example. Validate its prerequisites, tradeoffs and original CI environment against your repository before adapting it. - **[Stripe](https://starsling.dev/ci-playbooks/stripe#avoid-emulator-build-contention)**: Use it when Compilation runs while an emulator competes for the same CPU and memory. Check before adopting: Keep the device and ABI coverage other lanes require, and measure disk headroom before removing cleanup. ## Apply this technique ````text Evaluate and apply this CI technique to my repository: Build before starting the emulator. Compile the app first, then boot the emulator and install the finished build. Read the technique and its source-backed company examples: https://starsling.dev/ci-playbooks/techniques/avoid-emulator-build-contention.md Inspect this repository’s CI workflows, build and test commands, dependencies, and recent run timings. Identify where this technique applies and explain the expected benefit using this repository’s evidence. Measure a baseline from recent comparable runs: elapsed time, queue time, runner minutes and failures where available. If data is unavailable, say what cannot be measured. Compare relevant company approaches, checking prerequisites, platform differences and tradeoffs. Rank applicable options by evidence, fit and measurable opportunity; do not present company results as predictions for this repo. Recommend the smallest safe change, show what checks and fallback paths remain, and ASK ME WHICH CHANGE TO APPROVE BEFORE EDITING ANY FILES. Only after approval, work on a new feature branch, make one reversible change, and open a reviewable pull request. Never merge or push to a default or protected branch. Keep required checks, test coverage, deployment and release behavior intact. Validate the change and compare equivalent runs where possible; report limitations and what should be monitored after merge. ```` ## How Stripe used this technique Read what Stripe changed and follow the original sources. ### Stripe: Build before starting the emulator Stripe React Native moved app compilation ahead of emulator startup and installed the finished APK. It also built only the emulator’s x86_64 architecture and removed a disk-cleanup step, which the author estimated at 20 seconds. Evidence: Source PR/commit evidence Use it when: Compilation runs while an emulator competes for the same CPU and memory. Before applying it: Keep the device and ABI coverage other lanes require, and measure disk headroom before removing cleanup. [Read more in the Stripe playbook](https://starsling.dev/ci-playbooks/stripe#avoid-emulator-build-contention) [Primary source](https://github.com/stripe/stripe-react-native/pull/2111) ## CI optimization is continuous work. Apply this technique yourself, or use StarSling Runners for faster GitHub Actions and optional agent-driven optimization PRs, which teams on eligible paid plans can turn on. [Get self-improving CI](https://starsling.dev/products/runners) ## Related techniques ### [Build only what the test or analysis consumes](https://starsling.dev/ci-playbooks/techniques/build-only-consumed-inputs) Declare the build dependencies of each validation lane so unrelated targets do not join its critical path. 3 implementations · 2 companies (Stripe, Uber) ### [Install a pinned tool release](https://starsling.dev/ci-playbooks/techniques/pin-small-tool-install) Download one pinned, checksummed release in shared setup and skip the per-worker package-manager upgrade. 1 implementation · 1 company (Stripe) ### [Release query results before they become a timeout](https://starsling.dev/ci-playbooks/techniques/release-query-results) A query can finish while its unread response still holds the connection. 1 implementation · 1 company (Mastra) ## Company Playbooks ### [Anthropic](https://starsling.dev/ci-playbooks/anthropic) Run only affected tests ### [DoorDash](https://starsling.dev/ci-playbooks/doordash) Run build and test in parallel, sharded across CI agents ### [Linear](https://starsling.dev/ci-playbooks/linear) Benchmark the same job on faster hardware ### [Mastra](https://starsling.dev/ci-playbooks/mastra) StarSling runners for the slowest test workflow ### [OpenAI](https://starsling.dev/ci-playbooks/openai) Rank CI fixes by the minutes they save ### [Ramp](https://starsling.dev/ci-playbooks/ramp) Move a CPU-bound test suite to a faster CPU ### [Shopify](https://starsling.dev/ci-playbooks/shopify) Let an agent iterate against one CI metric ### [Spotify](https://starsling.dev/ci-playbooks/spotify) Build arm64 on native arm64 runners ### [Stripe](https://starsling.dev/ci-playbooks/stripe) Run only the tests a change can reach ### [Uber](https://starsling.dev/ci-playbooks/uber) Build the merge-queue speculations most likely to be needed ## Related guides Implementation guides for this technique. ### [Filter workflows by changed files](https://starsling.dev/best-practices/github-actions/path-filter-workflows) Use paths and job conditions while keeping required checks reporting. ### [Cancel superseded CI runs](https://starsling.dev/best-practices/github-actions/cancel-superseded-runs) Cancel obsolete PR runs with a correctly scoped concurrency group.