temporalio__skill-temporal-developer/references/php/determinism.md

PHP SDK Determinism

Overview

The PHP SDK does NOT have a sandbox like Python or TypeScript. There is no automatic enforcement of determinism — the developer must be disciplined. The SDK provides runtime command-ordering checks only.

Why Determinism Matters: History Replay

Temporal provides durable execution through History Replay. When a Worker needs to restore workflow state (after a crash, cache eviction, or to continue after a long timer), it re-executes the workflow code from the beginning, which requires the workflow code to be deterministic.

See references/core/determinism.md for the full explanation.

SDK Protection / Runtime Checking

The PHP SDK performs runtime checks that detect adding, removing, or reordering calls to:

• ExecuteActivity()
• ExecuteChildWorkflow()
• NewTimer()
• RequestCancelWorkflow()
• SideEffect()
• SignalExternalWorkflow()
• Sleep()

This is NOT a thorough check — it does not verify arguments or timer durations. Non-determinism that doesn't reorder commands will go undetected. Use replay testing to catch subtler issues.

Forbidden Operations

These must NOT be used in workflow code:

• No direct I/O: fopen(), file_get_contents(), curl_*, PDO, etc.
• No sleep() — use yield Workflow::timer(new \DateInterval('PT10S'))
• No time(), date(), microtime() — use Workflow::now()
• No rand(), random_int(), uniqid() — use yield Workflow::sideEffect()
• No blocking SPL functions
• No mutable global state

Testing Replay Compatibility

Use the WorkflowReplayer class to verify your code changes are compatible with existing histories. See the Workflow Replay Testing section of references/php/testing.md.

Best Practices

1. Use Workflow::now() for all time and date operations
2. Use yield Workflow::sideEffect() for any non-deterministic values
3. Delegate all I/O to activities
4. Test with WorkflowReplayer to catch non-determinism
5. Use Workflow::getLogger() instead of error_log() for replay-safe logging