os: add Process (#6786)

vlib/os/process_test.v

@@ -0,0 +1,63 @@
+import os
+import time
+
+fn test_getpid() {
+	pid := os.getpid()
+	eprintln('current pid: $pid')
+	assert pid != 0
+}
+
+fn test_run() {
+	if os.user_os() == 'windows' {
+		return
+	}
+	//
+	mut p := os.new_process('/bin/sleep')
+	p.set_args(['0.2'])
+	p.run()
+	assert p.status == .running
+	assert p.pid > 0
+	assert p.pid != os.getpid()
+	mut i := 0
+	for {
+		if !p.is_alive() {
+			break
+		}
+		os.system('ps -opid= -oppid= -ouser= -onice= -of= -ovsz= -orss= -otime= -oargs= -p $p.pid')
+		time.sleep_ms(50)
+		i++
+	}
+	p.wait()
+	assert p.code == 0
+	assert p.status == .exited
+	//
+	eprintln('polling iterations: $i')
+	assert i > 1
+	assert i < 20
+}
+
+fn test_wait() {
+	if os.user_os() == 'windows' {
+		return
+	}
+	mut p := os.new_process('/bin/date')
+	p.wait()
+	assert p.pid != os.getpid()
+	assert p.code == 0
+	assert p.status == .exited
+}
+
+fn test_slurping_output() {
+	if os.user_os() == 'windows' {
+		return
+	}
+	mut p := os.new_process('/bin/date')
+	p.set_redirect_stdio()
+	p.wait()
+	assert p.code == 0
+	assert p.status == .exited
+	output := p.stdout_slurp().trim_space()
+	errors := p.stderr_slurp().trim_space()
+	eprintln('p output: "$output"')
+	eprintln('p errors: "$errors"')
+}