Max spawn child processes rate at once

[PauliusSap]

Problem is when you need spawn very fast a lot of fpm child processes in the dynamic mode (pm = dynamic).
After every spawn it's make 1000ms pause (i think it's HEARTBEAT checker).
Child processes spawn algorithm growth x2 while exceed maximum spawn rate at this moment hardcoded value 32.
When you need spawn a lot of child processes you take a lot of time.

Example we have already spawned 3000 child processes at high load traffic need spawn fast +900 child processes.

[00:00:01] spawning 8 children, there are 0 idle, and 3008 total children 
[00:00:02] spawning 16 children, there are 0 idle, and 3024 total children <!-- algorithm growth x2
[00:00:03] spawning 32 children, there are 0 idle, and 3056 total children <!-- algorithm growth x2
[00:00:04] spawning 32 children, there are 0 idle, and 3088 total children <!-- reached maximum from this moment spawn only 32.
[00:00:05] spawning 32 children, there are 0 idle, and 3120 total children
...
...
[00:00:30] spawning 32 children, there are 0 idle, and 3920 total children <!-- Total exceed 30 seconds

Result is: we wait 30 seconds to spawn +920 child processes.

Summary: it's good to have this setting in the configuration because spawn new child processes don't have some heavy overhead.

[staabm]

Could you elaborate why/when you need to adjust this setting?

[cmb69]

cc @bukka

[bukka]

It looks good and think it makes sense to have an option for this. The code looks good as well. Just one thing - could you please add some basic test? I realise that a properly test this might be a bit flaky or a bit too have for CI env so maybe something just basic to at least check that it's possible to set it.

[PauliusSap]

It looks good and think it makes sense to have an option for this. The code looks good as well. Just one thing - could you please add some basic test? I realise that a properly test this might be a bit flaky or a bit too have for CI env so maybe something just basic to at least check that it's possible to set it.

@bukka I'm added a simple set test and merge commits.

[bukka]

Looks good. Just few minor things re the test.

[bukka]

Looks really good! Just few minor comments.

[bukka]

@PauliusSap Please could you then also squash it to a single commit.

[bukka]

And one more thing. Could you possibly also run fpm with this setting - possibly do one ping so it's kind of verified in the test that it's running. Something like extending config with

ping.path = /ping
ping.response = pong

and then add to the test something like

$tester = new FPM\Tester($cfg);
$tester->start();
$tester->expectLogStartNotices();
$tester->ping();
$tester->terminate();
$tester->expectLogTerminatingNotices();
$tester->close();

[PauliusSap]

And one more thing. Could you possibly also run fpm with this setting - possibly do one ping so it's kind of verified in the test that it's running. Something like extending config with

ping.path = /ping
ping.response = pong

and then add to the test something like

$tester = new FPM\Tester($cfg);
$tester->start();
$tester->expectLogStartNotices();
$tester->ping();
$tester->terminate();
$tester->expectLogTerminatingNotices();
$tester->close();

I use test argument. start(['-t', '-t']);

-t, --test Test FPM configuration and exit

Second -t argument meaning dump config.

[PauliusSap]

@PauliusSap Please could you then also squash it to a single commit.

Done

[bukka]

Merged via eac1609