workers fixes and improvements (#12863)

1 files changed, 47 insertions, 15 deletions

diff --git a/libnetdata/worker_utilization/README.md b/libnetdata/worker_utilization/README.md
index 85e532ed10..35f30b40b4 100644
--- a/libnetdata/worker_utilization/README.md
+++ b/libnetdata/worker_utilization/README.md
@@ -5,8 +5,16 @@ custom_edit_url: https://github.com/netdata/netdata/edit/master/libnetdata/onewa
 
 # Worker Utilization
 
-This library is to be used when there are 1 or more worker threads accepting requests of some kind and servicing them.
-The goal is to provide a very simple way to monitor worker threads utilization, as a percentage of the time they are busy and the amount of requests served.
+This library is to be used when there are 1 or more worker threads accepting requests
+of some kind and servicing them. The goal is to provide a very simple way to monitor
+worker threads utilization, as a percentage of the time they are busy and the amount
+of requests served.
+
+## Design goals
+
+1. Minimal, if any, impact on the performance of the workers
+2. Easy to be integrated into any kind of worker
+3. No state of any kind at the worker side
 
 ## How to use
 
@@ -19,40 +27,64 @@ void worker_register(const char *name);
 This will create the necessary structures for the library to work.
 No need to keep a pointer to them. They are allocated as `__thread` variables.
 
+Then job types need to be defined. Job types are anything a worker does that can be
+counted and their execution time needs to be reported. The library is fast enough to
+be integrated even on workers that perform hundreds of thousands of actions per second.
+
+Job types are defined like this:
+
+```c
+void worker_register_job_type(size_t id, const char *name);
+```
+
+`id` is a number starting from zero. The library is compiled with a fixed size of 50
+ids (0 to 49). More can be allocated by setting `WORKER_UTILIZATION_MAX_JOB_TYPES` in
+`worker_utilization.h`. `name` can be any string up to 22 characters. This can be
+changed by setting `WORKER_UTILIZATION_MAX_JOB_NAME_LENGTH` in `worker_utilization.h`.
+
+Each thread that calls `worker_register(name)` will allocate about 3kB for maintaining
+the information required.
+
 When the thread stops, call:
 
 ```c
-void worker_unregister(void)
+void worker_unregister(void);
 ```
 
 Again, no parameters, or return values.
 
+> IMPORTANT: cancellable threads need to add a call to `worker_unregister()` to the
+> `pop` function that cleans up the thread. Failure to do so, will result in about
+> 3kB of memory leak for every thread that is stopped.
+
 When you are about to do some work in the working thread, call:
 
 ```c
-void worker_is_busy(void)
+void worker_is_busy(size_t id);
 ```
 
 When you finish doing the job, call:
 
 ```c
-void worker_is_idle(void)
+void worker_is_idle(void);
 ```
 
-Calls to `worker_is_busy()` can be made one after another (without calling
+Calls to `worker_is_busy(id)` can be made one after another (without calling
 `worker_is_idle()` between them) to switch jobs without losing any time between
 them and eliminating one of the 2 clock calls involved.
 
 ## Implementation details
 
-Totally lockless, extremely fast, it should not introduce any kind of problems to the workers.
-Every time `worker_is_busy()` or `worker_is_idle()` are called, a call to `now_realtime_usec()`
-is done and a couple of variables are updated. That's it!
+Totally lockless, extremely fast, it should not introduce any kind of problems to the
+workers. Every time `worker_is_busy(id)` or `worker_is_idle()` are called, a call to
+`now_realtime_usec()` is done and a couple of variables are updated. That's it!
 
-The worker does not need to update the variables regularly. Based on the last status of the worker,
-the statistics collector of netdata will calculate if the thread is busy or idle all the time or
-part of the time. Works well for both thousands of jobs per second and unlimited working time
-(being totally busy with a single request for ages).
+The worker does not need to update the variables regularly. Based on the last status
+of the worker, the statistics collector of netdata will calculate if the thread is
+busy or idle all the time or part of the time. Works well for both thousands of jobs
+per second and unlimited working time (being totally busy with a single request for
+ages).
 
-The statistics collector is called by the global statistics thread of netdata. So, even if the workers
-are extremely busy with their jobs, netdata will be able to know how busy they are.
+The statistics collector is called by the global statistics thread of netdata. So,
+even if the workers are extremely busy with their jobs, netdata will be able to know
+how busy they are.