zx_system_watch_memory_stall

Summary

Retrieve an event that becomes signaled if the memory stall level exceeds a given threshold over a time window.

Declaration

#include <zircon/syscalls-next.h>

zx_status_t zx_system_watch_memory_stall(zx_handle_t resource,
                                         zx_system_memory_stall_type_t kind,
                                         zx_duration_mono_t threshold,
                                         zx_duration_mono_t window,
                                         zx_handle_t* event);

Description

resource must be a handle to the stall resource.

kind must be one of the following (see the ZX_INFO_MEMORY_STALL in zx_object_get_info()):

ZX_SYSTEM_MEMORY_STALL_SOME
ZX_SYSTEM_MEMORY_STALL_FULL

threshold is minimum stall time that will trigger the signal.

window is the duration of the observation window.

It must hold that 0 < threshold <= window <= 10 seconds.

The kernel will set (ZX_EVENT_SIGNALED) on the returned event if the watched stall timer grew by at least threshold during the last window, and clear it once it is no longer the case.

Rights

Caller job policy must allow ZX_POL_NEW_EVENT.

Return value

zx_system_watch_memory_stall() returns ZX_OK on success, and event will be a valid handle, or an error code from below on failure.

Errors

ZX_ERR_BAD_HANDLE resource is not a valid handle.

ZX_ERR_WRONG_TYPE resource is not resource kind ZX_RSRC_KIND_SYSTEM.

ZX_ERR_OUT_OF_RANGE resource is not in the range [ZX_RSRC_SYSTEM_STALL_BASE, ZX_RSRC_SYSTEM_STALL_BASE+1).

ZX_ERR_INVALID_ARGS kind is not one of the above values.

ZX_ERR_INVALID_ARGS threshold or window are not in the allowed range.

ZX_ERR_NO_MEMORY Failure due to lack of memory. There is no good way for userspace to handle this (unlikely) error. In a future build this error will no longer occur.

Notes

Even the API defines threshold and window as the duration type (that is, in nanoseconds), the kernel may not use the full precision of the requested values.