runtime: add the MAXPROCS function

std/runtime/thread.jule

@@ -51,9 +51,15 @@ const threadSC_EmptySelect = 1 << 0
 // in the threads. Subsequent thread generations may use the same allocation
 // of closed threads for the new spawned threads.
 // threadCases stores special cases for thread management.
+// maxprocs stores total number of logical threads.
 static threadMutex = fmutex{}
 static mut threads = (&thread)(nil)
 static mut threadCases = threadSC_NA
+static mut maxprocs = 0
+
+// Returns the number of cores.
+// Returns zero until data initialized by the runtime.
+fn MAXPROCS(): int { ret maxprocs }
 
 // Allocates a new thread and sets state as running.
 fn newThread(): &thread {

std/runtime/thread_unix.jule

@@ -12,6 +12,7 @@ cpp fn pthread_equal(cpp.pthread_t, cpp.pthread_t): bool
 cpp fn pthread_detach(cpp.pthread_t): int
 cpp fn pthread_self(): cpp.pthread_t
 cpp fn sched_yield(): int
+cpp fn sysconf(name: integ::Int): integ::Long
 
 #typedef
 cpp struct pthread_t{}
@@ -66,6 +67,8 @@ fn init() {
 	// Push the main thread to threads.
 	// See the documentation of the pushNewThread function.
 	threadMutex.lock()
+	// We already locked the mutex, set maxproc too.
+	maxprocs = unsafe { int(cpp.sysconf(_SC_NPROCESSORS_ONLN)) }
 	mut t := newThread()
 	t.os.handle = currentThreadID()
 	threads = t

std/runtime/thread_windows.jule

@@ -67,6 +67,12 @@ fn init() {
 	// Push the main thread to threads.
 	// See the documentation of the pushNewThread function.
 	threadMutex.lock()
+	{
+		// We already locked the mutex, set maxproc too.
+		let info: cpp.SYSTEM_INFO
+		unsafe { cpp.GetSystemInfo(&info) }
+		maxprocs = int(info.dwNumberOfProcessors)
+	}
 	mut t := newThread()
 	t.os.id = currentThreadID()
 	threads = t