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backtrace

Note

This is a point-in-time snapshot of the API documentation from January 2026. Going forward, we will not be maintaining a public copy of these references, and recommend users to refer to the built-in signature helpers available in the Hack LSP instead for complete and up-to-date information.

Generates a backtrace for $awaitable

namespace HH\Asio;

function backtrace<T>(
  Awaitable<T, mixed> $awaitable,
  int $options = \DEBUG_BACKTRACE_PROVIDE_OBJECT,
  int $limit = 0,
): varray<dict<string, mixed>, darray>;

Following conditions must be met to produce non-empty backtrace:

  • $awaitable has not finished yet (i.e. has_finished($awaitable) === false)
  • $awaitable is part of valid scheduler context (i.e. $awaitable->getContextIdx() > 0) If either condition is not met, backtrace() returns empty array.

Parameters​

  • Awaitable<T,mixed> $awaitable - Awaitable, to take backtrace from.
  • int $options = \DEBUG_BACKTRACE_PROVIDE_OBJECT - bitmask of the following options: DEBUG_BACKTRACE_PROVIDE_OBJECT DEBUG_BACKTRACE_PROVIDE_METADATA DEBUG_BACKTRACE_IGNORE_ARGS
  • int $limit = 0 - the maximum number of stack frames returned. By default (limit=0) it returns all stack frames.

Returns​

  • array - - Returns an array of associative arrays. See debug_backtrace() for detailed format description.