| # Counter |
| |
| ## NAME |
| |
| counter - A semaphore-like object for synchronizing across processes |
| |
| ## SYNOPSIS |
| |
| A counter is like an [event], but with an integer that can be incremented, |
| decremented, read, or written. |
| |
| ## DESCRIPTION |
| |
| Counter is a synchronization tool allowing processes to coordinate and |
| synchronize their actions. A counter contains a signed 64-bit integer and is |
| somewhat similar to a counting semaphore. |
| |
| Counter is designed to be used with [`zx_object_wait_one()`], |
| [`zx_object_wait_many()`], or [`zx_object_wait_async()`]. |
| |
| ## SIGNALS |
| |
| In addition to the standard user signals (**ZX_USER_SIGNAL_0** through |
| **ZX_USER_SIGNAL_7**), counter has two signals that are automatically |
| asserted/deasserted based on the value: |
| |
| **ZX_COUNTER_NON_POSITIVE** indicates the value is less than or equal to zero. |
| |
| **ZX_COUNTER_POSITIVE** indicates the value is greater than or equal to zero. |
| |
| ## SYSCALLS |
| - [`zx_counter_create()`] - create a counter |
| - [`zx_counter_add()`] - add to a counter |
| - [`zx_counter_read()`] - read a counter's value |
| - [`zx_counter_write()`] - write a counter's value |
| |
| |
| [event]: /reference/kernel_objects/event.md |
| [`zx_counter_create()`]: /reference/syscalls/counter_create.md |
| [`zx_counter_add()`]: /reference/syscalls/counter_add.md |
| [`zx_counter_read()`]: /reference/syscalls/counter_read.md |
| [`zx_counter_write()`]: /reference/syscalls/counter_write.md |
| [`zx_object_wait_one()`]: /reference/syscalls/object_wait_one.md |
| [`zx_object_wait_many()`]: /reference/syscalls/object_wait_many.md |
| [`zx_object_wait_async()`]: /reference/syscalls/object_wait_async.md |
