On 20/03/2017 15:40, Corinna Vinschen wrote:
On Mar 20 15:04, Jon Turney wrote:
On 20/03/2017 10:37, Corinna Vinschen wrote:
On Mar 17 17:50, Jon Turney wrote:
The load average is global, non-critical data. So what about storing it
in shared_info instead? This way, only the first call of the first
Cygwin process returns all zero.
Ok.
+static bool load_init (void)
+{
+ static bool tried = false;
+ static bool initialized = false;
+
+ if (!tried) {
+ tried = true;
+
+ if ((PdhOpenQueryA (NULL, 0, &query) == ERROR_SUCCESS) &&
+ (PdhAddEnglishCounterA (query, "\\Processor(_Total)\\% Processor Time",
+ 0, &counter1) == ERROR_SUCCESS) &&
+ (PdhAddEnglishCounterA (query, "\\System\\Processor Queue Length",
+ 0, &counter2) == ERROR_SUCCESS)) {
+ initialized = true;
+ } else {
+ debug_printf("loadavg PDH initialization failed\n");
+ }
+ }
+
+ return initialized;
+}
How slow is that initialization? Would it {make sense|hurt} to call it
once in the initalization of Cygwin's shared mem in shared_info::initialize?
I don't think that's particularly heavyweight, and I didn't see anything to
suggest that PDH query handles can be shared between processes, but I'll
look into it.
Oh, right, that might pose a problem.
I can't find anything which documents these handles as shareable.
In practise, they seem to randomly stop working after a while after the
process which created the handle exits, or something like that. :S
But even then:
The first process creating shared_info could call this and prime the values
with a first call to getloadavg. Each other process would have to init its
We cannot determine an initial value of load when shared_info is
created, as the %CPU is not measured instantaneously, but over an
interval. This means that we can't have a load estimate until the 2nd
time a process calls PdhCollectQueryData()
I've tweaked things slightly in v2 so the loadavg is initialized to the
current load, rather than converging on it from 0.0.
