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fb_setprofile

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.

Set a callback function to be called whenever a function is entered or exited

function fb_setprofile(
  mixed $callback,
  int $flags = SETPROFILE_FLAGS_DEFAULT,
  vec<string> $functions = vec [
],
): void;

Takes 3 args, the function name, the mode (enter or exit), and an array describing the frame.

Parameters​

  • mixed $callback - Profiler function to call or null to disable
  • int $flags = SETPROFILE_FLAGS_DEFAULT - Controls when it should get called back and with what
  • vec<string> $functions = vec [ ] - Only receive callbacks on these functions. In effect only when it's not empty.

Returns​

  • void