Add support for thread data parsing.

testdata/fixtures.ttar

@@ -806,6 +806,57 @@ voluntary_ctxt_switches:	4742839
 nonvoluntary_ctxt_switches:	1727500
 Mode: 644
 # ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Directory: fixtures/proc/27079
+Mode: 755
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Path: fixtures/proc/27079/stat
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+Mode: 644
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+Directory: fixtures/proc/27079/task
+Mode: 755
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Directory: fixtures/proc/27079/task/27079
+Mode: 755
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Path: fixtures/proc/27079/task/27079/stat
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+Mode: 644
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Directory: fixtures/proc/27079/task/27080
+Mode: 755
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Path: fixtures/proc/27079/task/27080/stat
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+Mode: 644
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Directory: fixtures/proc/27079/task/27081
+Mode: 755
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Path: fixtures/proc/27079/task/27081/stat
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+Mode: 644
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Directory: fixtures/proc/27079/task/27082
+Mode: 755
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Path: fixtures/proc/27079/task/27082/stat
+Lines: 1
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+Mode: 644
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Directory: fixtures/proc/27079/task/27083
+Mode: 755
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Path: fixtures/proc/27079/task/27083/stat
+Lines: 1
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+Mode: 644
+# ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 Directory: fixtures/proc/584
 Mode: 755
 # ttar - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

thread.go

@@ -0,0 +1,79 @@
+// Copyright 2022 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 procfs
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+
+	fsi "github.com/prometheus/procfs/internal/fs"
+)
+
+// Provide access to /proc/PID/task/TID files, for thread specific values. Since
+// such files have the same structure as /proc/PID/ ones, the data structures
+// and the parsers for the latter may be reused.
+
+// AllThreads returns a list of all currently available threads under /proc/PID.
+func AllThreads(pid int) (Procs, error) {
+	fs, err := NewFS(DefaultMountPoint)
+	if err != nil {
+		return Procs{}, err
+	}
+	return fs.AllThreads(pid)
+}
+
+// AllThreads returns a list of all currently available threads for PID.
+func (fs FS) AllThreads(pid int) (Procs, error) {
+	taskPath := fs.proc.Path(strconv.Itoa(pid), "task")
+	d, err := os.Open(taskPath)
+	if err != nil {
+		return Procs{}, err
+	}
+	defer d.Close()
+
+	names, err := d.Readdirnames(-1)
+	if err != nil {
+		return Procs{}, fmt.Errorf("could not read %q: %w", d.Name(), err)
+	}
+
+	t := Procs{}
+	for _, n := range names {
+		tid, err := strconv.ParseInt(n, 10, 64)
+		if err != nil {
+			continue
+		}
+		t = append(t, Proc{PID: int(tid), fs: fsi.FS(taskPath)})
+	}
+
+	return t, nil
+}
+
+// Thread returns a process for a given PID, TID.
+func (fs FS) Thread(pid, tid int) (Proc, error) {
+	taskPath := fs.proc.Path(strconv.Itoa(pid), "task")
+	if _, err := os.Stat(taskPath); err != nil {
+		return Proc{}, err
+	}
+	return Proc{PID: tid, fs: fsi.FS(taskPath)}, nil
+}
+
+// Thread returns a process for a given TID of Proc.
+func (proc Proc) Thread(tid int) (Proc, error) {
+	tfs := fsi.FS(proc.path("task"))
+	if _, err := os.Stat(tfs.Path(strconv.Itoa(tid))); err != nil {
+		return Proc{}, err
+	}
+	return Proc{PID: tid, fs: tfs}, nil
+}

thread_test.go

@@ -0,0 +1,114 @@
+// Copyright 2022 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 procfs
+
+import (
+	"reflect"
+	"sort"
+	"strconv"
+	"testing"
+)
+
+var (
+	testPID  = int(27079)
+	testTIDS = [...]int{27079, 27080, 27081, 27082, 27083}
+)
+
+func TestAllThreads(t *testing.T) {
+	fixFS := getProcFixtures(t)
+	threads, err := fixFS.AllThreads(testPID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	sort.Sort(threads)
+	for i, tid := range testTIDS {
+		if wantTID, haveTID := tid, threads[i].PID; wantTID != haveTID {
+			t.Errorf("want TID %d, have %d", wantTID, haveTID)
+		}
+		wantFS := fixFS.proc.Path(strconv.Itoa(testPID), "task")
+		haveFS := string(threads[i].fs)
+		if wantFS != haveFS {
+			t.Errorf("want fs %q, have %q", wantFS, haveFS)
+		}
+	}
+}
+
+func TestThreadStat(t *testing.T) {
+	// Pull process and thread stats.
+	proc, err := getProcFixtures(t).Proc(testPID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	procStat, err := proc.Stat()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	threads, err := getProcFixtures(t).AllThreads(testPID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	sort.Sort(threads)
+	threadStats := make([]*ProcStat, len(threads))
+	for i, thread := range threads {
+		threadStat, err := thread.Stat()
+		if err != nil {
+			t.Fatal(err)
+		}
+		threadStats[i] = &threadStat
+	}
+
+	// The following fields should be shared between the process and its thread:
+	procStatValue := reflect.ValueOf(procStat)
+	sharedFields := [...]string{
+		"PPID",
+		"PGRP",
+		"Session",
+		"TTY",
+		"TPGID",
+		"VSize",
+		"RSS",
+	}
+
+	for i, thread := range threads {
+		threadStatValue := reflect.ValueOf(threadStats[i]).Elem()
+		for _, f := range sharedFields {
+			if want, have := procStatValue.FieldByName(f), threadStatValue.FieldByName(f); want.Interface() != have.Interface() {
+				t.Errorf("TID %d, want %s %#v, have %#v", thread.PID, f, want, have)
+			}
+		}
+	}
+
+	// Thread specific fields:
+	for i, thread := range threads {
+		if want, have := thread.PID, threadStats[i].PID; want != have {
+			t.Errorf("TID %d, want PID %d, have %d", thread.PID, want, have)
+		}
+	}
+
+	// Finally exemplify the relationship between process and constituent
+	// threads CPU times: each the former  ~ the sum of the corresponding
+	// latter. Require -v flag.
+	totalUTime, totalSTime := uint(0), uint(0)
+	for _, thread := range threads {
+		threadStat, err := thread.Stat()
+		if err != nil {
+			t.Fatal(err)
+		}
+		t.Logf("TID %d, UTime %d, STime %d", thread.PID, threadStat.UTime, threadStat.STime)
+		totalUTime += threadStat.UTime
+		totalSTime += threadStat.STime
+	}
+	t.Logf("PID %d, UTime %d, STime %d, total threads UTime %d, STime %d", proc.PID, procStat.UTime, procStat.STime, totalUTime, totalSTime)
+}