runtime: implement NumCPU for -scheduler=threads

For the threads scheduler, it makes sense to have NumCPU available.
For all other schedulers, the number of available CPUs is practically
limited to one by the scheduler (even though the system might have more
CPUs).

GNUmakefile

@@ -972,6 +972,7 @@ endif
 	@cp -rp lib/musl/crt/crt1.c          build/release/tinygo/lib/musl/crt
 	@cp -rp lib/musl/COPYRIGHT           build/release/tinygo/lib/musl
 	@cp -rp lib/musl/include             build/release/tinygo/lib/musl
+	@cp -rp lib/musl/src/conf            build/release/tinygo/lib/musl/src
 	@cp -rp lib/musl/src/ctype           build/release/tinygo/lib/musl/src
 	@cp -rp lib/musl/src/env             build/release/tinygo/lib/musl/src
 	@cp -rp lib/musl/src/errno           build/release/tinygo/lib/musl/src

builder/musl.go

@@ -124,6 +124,7 @@ var libMusl = Library{
 	librarySources: func(target string) ([]string, error) {
 		arch := compileopts.MuslArchitecture(target)
 		globs := []string{
+			"conf/*.c",
 			"ctype/*.c",
 			"env/*.c",
 			"errno/*.c",

compileopts/config.go

@@ -22,7 +22,7 @@ import (
 // builder.Library struct but that's hard to do since we want to know the
 // library path in advance in several places).
 var libVersions = map[string]int{
-	"musl": 2,
+	"musl": 3,
 }
 
 // Config keeps all configuration affecting the build in a single struct.

src/internal/task/task_threads.c

@@ -6,6 +6,7 @@
 #include <signal.h>
 #include <stdint.h>
 #include <stdio.h>
+#include <unistd.h>
 
 // BDWGC also uses SIGRTMIN+6 on Linux, which seems like a reasonable choice.
 #ifdef __linux__
@@ -29,7 +30,7 @@ struct state_pass {
 void tinygo_task_gc_pause(int sig);
 
 // Initialize the main thread.
-void tinygo_task_init(void *mainTask, pthread_t *thread, void *context) {
+void tinygo_task_init(void *mainTask, pthread_t *thread, int *numCPU, void *context) {
     // Make sure the current task pointer is set correctly for the main
     // goroutine as well.
     current_task = mainTask;
@@ -43,6 +44,14 @@ void tinygo_task_init(void *mainTask, pthread_t *thread, void *context) {
     act.sa_flags = SA_SIGINFO;
     act.sa_handler = &tinygo_task_gc_pause;
     sigaction(taskPauseSignal, &act, NULL);
+
+    // Obtain the number of CPUs available on program start (for NumCPU).
+    int num = sysconf(_SC_NPROCESSORS_ONLN);
+    if (num <= 0) {
+        // Fallback in case there is an error.
+        num = 1;
+    }
+    *numCPU = num;
 }
 
 void tinygo_task_exited(void*);

src/internal/task/task_threads.go

@@ -38,6 +38,8 @@ type state struct {
 // Goroutine counter, starting at 0 for the main goroutine.
 var goroutineID uintptr
 
+var numCPU int32
+
 var mainTask Task
 
 // Queue of tasks (see QueueNext) that currently exist in the program.
@@ -53,7 +55,7 @@ func OnSystemStack() bool {
 // startup, before starting any other goroutines.
 func Init(sp uintptr) {
 	mainTask.state.stackTop = sp
-	tinygo_task_init(&mainTask, &mainTask.state.thread)
+	tinygo_task_init(&mainTask, &mainTask.state.thread, &numCPU)
 }
 
 // Return the task struct for the current thread.
@@ -259,7 +261,7 @@ func runtimePanic(msg string)
 // that the 't' parameter won't escape (because it will).
 //
 //go:linkname tinygo_task_init tinygo_task_init
-func tinygo_task_init(t *Task, thread *threadID)
+func tinygo_task_init(t *Task, thread *threadID, numCPU *int32)
 
 // Here same as for tinygo_task_init.
 //
@@ -273,3 +275,7 @@ func tinygo_task_send_gc_signal(threadID)
 
 //export tinygo_task_current
 func tinygo_task_current() unsafe.Pointer
+
+func NumCPU() int {
+	return int(numCPU)
+}

src/runtime/debug.go

@@ -1,14 +1,5 @@
 package runtime
 
-// NumCPU returns the number of logical CPUs usable by the current process.
-//
-// The set of available CPUs is checked by querying the operating system
-// at process startup. Changes to operating system CPU allocation after
-// process startup are not reflected.
-func NumCPU() int {
-	return 1
-}
-
 // Stub for NumCgoCall, does not return the real value
 func NumCgoCall() int {
 	return 0

src/runtime/scheduler_cooperative.go

@@ -60,6 +60,11 @@ func Gosched() {
 	task.Pause()
 }
 
+// NumCPU returns the number of logical CPUs usable by the current process.
+func NumCPU() int {
+	return 1
+}
+
 // Add this task to the sleep queue, assuming its state is set to sleeping.
 func addSleepTask(t *task.Task, duration timeUnit) {
 	if schedulerDebug {

src/runtime/scheduler_none.go

@@ -44,6 +44,11 @@ func Gosched() {
 	// There are no other goroutines, so there's nothing to schedule.
 }
 
+// NumCPU returns the number of logical CPUs usable by the current process.
+func NumCPU() int {
+	return 1
+}
+
 func addTimer(tim *timerNode) {
 	runtimePanic("timers not supported without a scheduler")
 }

src/runtime/scheduler_threads.go

@@ -50,6 +50,11 @@ func Gosched() {
 	// operation, so is probably best not to use.
 }
 
+// NumCPU returns the number of logical CPUs usable by the current process.
+func NumCPU() int {
+	return task.NumCPU()
+}
+
 // Separate goroutine (thread) that runs timer callbacks when they expire.
 func timerRunner() {
 	for {