process_collector: fill in most statistics on macOS (#1600)

* process_collector: fill in most statistics on macOS

Unfortunately, the virtual memory, resident memory, and network stats will
require access to undocumented C functions.  I was warned off of cgo in IRC
because it would then have to be enabled in a bunch of different projects that
use this module, but I already was against it because that would break the
ability to cross-compile.  There is no interface to `dlopen` built into golang.
The `github.com/ebitengine/purego` module looks promising (I can cross-compile
and call these methods), but I'm currently getting unexpected results.  I'll
follow up with that separately if I can get it working, but hopefully this stuff
is pretty uncontroversial.

Tested on macOS 10.14.6 (amd64), macOS 14.6.1 (amd64), and macOS 15.0 (arm64)
by spawning `/usr/bin/ulimit -a -S` and `/usr/sbin/lsof -c $my_process` from
the test exporter process, and `ps -o lstart,vsize,rss,utime,stime,command` from
the shell, and comparing results with the exported metrics.

I can't find documentation for `RLIMIT_AS` on macOS (specifically if it's in
bytes or pages).  It's currently being reported back as `RLIM_INFINITY`, which
seems reasonable, because I've come across reports that the value is ignored
anyway[1].  The bash 3.2 code for the built-in `ulimit` divides the value
reported by `getrusage(2)` by 1024 when printing, as it does for `RLIMIT_DATA`,
which is documented as being bytes in `getrusage(2)`.  The help for `ulimit`
indicates it prints both in kbytes, so it's reasonable to assume this is already
in bytes.

[1] https://issues.chromium.org/issues/40581251#comment3

Signed-off-by: Matt Harbison <mharbison72@gmail.com>

* Update prometheus/process_collector_darwin.go

Co-authored-by: Ben Kochie <superq@gmail.com>
Signed-off-by: Matt Harbison <57785103+mharbison72@users.noreply.github.com>

---------

Signed-off-by: Matt Harbison <mharbison72@gmail.com>
Signed-off-by: Matt Harbison <57785103+mharbison72@users.noreply.github.com>
Co-authored-by: Ben Kochie <superq@gmail.com>
Co-authored-by: Bartlomiej Plotka <bwplotka@gmail.com>

prometheus/process_collector_darwin.go

@@ -0,0 +1,110 @@
+// Copyright 2024 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package prometheus
+
+import (
+	"fmt"
+	"golang.org/x/sys/unix"
+	"os"
+	"syscall"
+	"time"
+)
+
+func canCollectProcess() bool {
+	return true
+}
+
+func getSoftLimit(which int) (uint64, error) {
+	rlimit := syscall.Rlimit{}
+
+	if err := syscall.Getrlimit(which, &rlimit); err != nil {
+		return 0, err
+	}
+
+	return rlimit.Cur, nil
+}
+
+func getOpenFileCount() (float64, error) {
+	// Alternately, the undocumented proc_pidinfo(PROC_PIDLISTFDS) can be used to
+	// return a list of open fds, but that requires a way to call C APIs.  The
+	// benefits, however, include fewer system calls and not failing when at the
+	// open file soft limit.
+
+	if dir, err := os.Open("/dev/fd"); err != nil {
+		return 0.0, err
+	} else {
+		defer dir.Close()
+
+		// Avoid ReadDir(), as it calls stat(2) on each descriptor.  Not only is
+		// that info not used, but KQUEUE descriptors fail stat(2), which causes
+		// the whole method to fail.
+		if names, err := dir.Readdirnames(0); err != nil {
+			return 0.0, err
+		} else {
+			// Subtract 1 to ignore the open /dev/fd descriptor above.
+			return float64(len(names) - 1), nil
+		}
+	}
+}
+
+func (c *processCollector) processCollect(ch chan<- Metric) {
+	if procs, err := unix.SysctlKinfoProcSlice("kern.proc.pid", os.Getpid()); err == nil {
+		if len(procs) == 1 {
+			startTime := float64(procs[0].Proc.P_starttime.Nano() / 1e9)
+			ch <- MustNewConstMetric(c.startTime, GaugeValue, startTime)
+		} else {
+			err = fmt.Errorf("sysctl() returned %d proc structs (expected 1)", len(procs))
+			c.reportError(ch, c.startTime, err)
+		}
+	} else {
+		c.reportError(ch, c.startTime, err)
+	}
+
+	// The proc structure returned by kern.proc.pid above has an Rusage member,
+	// but it is not filled in, so it needs to be fetched by getrusage(2).  For
+	// that call, the UTime, STime, and Maxrss members are filled out, but not
+	// Ixrss, Idrss, or Isrss for the memory usage.  Memory stats will require
+	// access to the C API to call task_info(TASK_BASIC_INFO).
+	rusage := unix.Rusage{}
+
+	if err := unix.Getrusage(syscall.RUSAGE_SELF, &rusage); err == nil {
+		cpuTime := time.Duration(rusage.Stime.Nano() + rusage.Utime.Nano()).Seconds()
+		ch <- MustNewConstMetric(c.cpuTotal, CounterValue, cpuTime)
+	} else {
+		c.reportError(ch, c.cpuTotal, err)
+	}
+
+	// TODO: publish c.vsize and c.rss values
+
+	if fds, err := getOpenFileCount(); err == nil {
+		ch <- MustNewConstMetric(c.openFDs, GaugeValue, fds)
+	} else {
+		c.reportError(ch, c.openFDs, err)
+	}
+
+	if openFiles, err := getSoftLimit(syscall.RLIMIT_NOFILE); err == nil {
+		ch <- MustNewConstMetric(c.maxFDs, GaugeValue, float64(openFiles))
+	} else {
+		c.reportError(ch, c.maxFDs, err)
+	}
+
+	if addressSpace, err := getSoftLimit(syscall.RLIMIT_AS); err == nil {
+		ch <- MustNewConstMetric(c.maxVsize, GaugeValue, float64(addressSpace))
+	} else {
+		c.reportError(ch, c.maxVsize, err)
+	}
+
+	// TODO: socket(PF_SYSTEM) to fetch "com.apple.network.statistics" might
+	//  be able to get the per-process network send/receive counts.
+}

prometheus/process_collector_other.go

@@ -11,8 +11,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-//go:build !windows && !js && !wasip1
+//go:build !windows && !js && !wasip1 && !darwin
-// +build !windows,!js,!wasip1
+// +build !windows,!js,!wasip1,!darwin
 
 package prometheus