src/pkg/runtime/darwin/thread.c - go - Git at Google

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 #include "runtime.h"
 #include "defs.h"
 #include "os.h"
 #include "stack.h"

 extern SigTab runtime·sigtab[];

 static void
 unimplemented(int8 *name)
 {
 	runtime·prints(name);
 	runtime·prints(" not implemented\n");
 	*(int32*)1231 = 1231;
 }

 // Thread-safe allocation of a semaphore.
 // Psema points at a kernel semaphore key.
 // It starts out zero, meaning no semaphore.
 // Fill it in, being careful of others calling initsema
 // simultaneously.
 static void
 initsema(uint32 *psema)
 {
 	uint32 sema;

 	if(*psema != 0)	// already have one
 		return;

 	sema = runtime·mach_semcreate();
 	if(!runtime·cas(psema, 0, sema)){
 		// Someone else filled it in.  Use theirs.
 		runtime·mach_semdestroy(sema);
 		return;
 	}
 }


 // Blocking locks.

 // Implement Locks, using semaphores.
 // l->key is the number of threads who want the lock.
 // In a race, one thread increments l->key from 0 to 1
 // and the others increment it from >0 to >1.  The thread
 // who does the 0->1 increment gets the lock, and the
 // others wait on the semaphore.  When the 0->1 thread
 // releases the lock by decrementing l->key, l->key will
 // be >0, so it will increment the semaphore to wake up
 // one of the others.  This is the same algorithm used
 // in Plan 9's user-level locks.

 void
 runtime·lock(Lock *l)
 {
 	if(m->locks < 0)
 		runtime·throw("lock count");
 	m->locks++;

 	if(runtime·xadd(&l->key, 1) > 1) {	// someone else has it; wait
 		// Allocate semaphore if needed.
 		if(l->sema == 0)
 			initsema(&l->sema);
 		runtime·mach_semacquire(l->sema);
 	}
 }

 void
 runtime·unlock(Lock *l)
 {
 	m->locks--;
 	if(m->locks < 0)
 		runtime·throw("lock count");

 	if(runtime·xadd(&l->key, -1) > 0) {	// someone else is waiting
 		// Allocate semaphore if needed.
 		if(l->sema == 0)
 			initsema(&l->sema);
 		runtime·mach_semrelease(l->sema);
 	}
 }

 static void
 destroylock(Lock *l)
 {
 	if(l->sema != 0) {
 		runtime·mach_semdestroy(l->sema);
 		l->sema = 0;
 	}
 }

 // User-level semaphore implementation:
 // try to do the operations in user space on u,
 // but when it's time to block, fall back on the kernel semaphore k.
 // This is the same algorithm used in Plan 9.
 void
 runtime·usemacquire(Usema *s)
 {
 	if((int32)runtime·xadd(&s->u, -1) < 0) {
 		if(s->k == 0)
 			initsema(&s->k);
 		runtime·mach_semacquire(s->k);
 	}
 }

 void
 runtime·usemrelease(Usema *s)
 {
 	if((int32)runtime·xadd(&s->u, 1) <= 0) {
 		if(s->k == 0)
 			initsema(&s->k);
 		runtime·mach_semrelease(s->k);
 	}
 }


 // Event notifications.
 void
 runtime·noteclear(Note *n)
 {
 	n->wakeup = 0;
 }

 void
 runtime·notesleep(Note *n)
 {
 	while(!n->wakeup)
 		runtime·usemacquire(&n->sema);
 }

 void
 runtime·notewakeup(Note *n)
 {
 	n->wakeup = 1;
 	runtime·usemrelease(&n->sema);
 }


 // BSD interface for threading.
 void
 runtime·osinit(void)
 {
 	// Register our thread-creation callback (see {amd64,386}/sys.s)
 	// but only if we're not using cgo.  If we are using cgo we need
 	// to let the C pthread libary install its own thread-creation callback.
 	if(!runtime·iscgo)
 		runtime·bsdthread_register();
 	runtime·destroylock = destroylock;

 	// Use sysctl to fetch hw.ncpu.
 	uint32 mib[2];
 	uint32 out;
 	int32 ret;
 	uintptr nout;

 	mib[0] = 6;
 	mib[1] = 3;
 	nout = sizeof out;
 	out = 0;
 	ret = runtime·sysctl(mib, 2, (byte*)&out, &nout, nil, 0);
 	if(ret >= 0)
 		runtime·ncpu = out;
 }

 void
 runtime·goenvs(void)
 {
 	runtime·goenvs_unix();
 }

 void
 runtime·newosproc(M *m, G *g, void *stk, void (*fn)(void))
 {
 	int32 errno;

 	m->tls[0] = m->id;	// so 386 asm can find it
 	if(0){
 		runtime·printf("newosproc stk=%p m=%p g=%p fn=%p id=%d/%d ostk=%p\n",
 			stk, m, g, fn, m->id, m->tls[0], &m);
 	}
 	if((errno = runtime·bsdthread_create(stk, m, g, fn)) < 0) {
 		runtime·printf("runtime: failed to create new OS thread (have %d already; errno=%d)\n", runtime·mcount(), -errno);
 		runtime·throw("runtime.newosproc");
 	}
 }

 // Called to initialize a new m (including the bootstrap m).
 void
 runtime·minit(void)
 {
 	// Initialize signal handling.
 	m->gsignal = runtime·malg(32*1024);	// OS X wants >=8K, Linux >=2K
 	runtime·signalstack(m->gsignal->stackguard - StackGuard, 32*1024);
 }

 // Mach IPC, to get at semaphores
 // Definitions are in /usr/include/mach on a Mac.

 static void
 macherror(int32 r, int8 *fn)
 {
 	runtime·printf("mach error %s: %d\n", fn, r);
 	runtime·throw("mach error");
 }

 enum
 {
 	DebugMach = 0
 };

 static MachNDR zerondr;

 #define MACH_MSGH_BITS(a, b) ((a) | ((b)<<8))

 static int32
 mach_msg(MachHeader *h,
 	int32 op,
 	uint32 send_size,
 	uint32 rcv_size,
 	uint32 rcv_name,
 	uint32 timeout,
 	uint32 notify)
 {
 	// TODO: Loop on interrupt.
 	return runtime·mach_msg_trap(h, op, send_size, rcv_size, rcv_name, timeout, notify);
 }

 // Mach RPC (MIG)

 enum
 {
 	MinMachMsg = 48,
 	Reply = 100,
 };

 #pragma pack on
 typedef struct CodeMsg CodeMsg;
 struct CodeMsg
 {
 	MachHeader h;
 	MachNDR NDR;
 	int32 code;
 };
 #pragma pack off

 static int32
 machcall(MachHeader *h, int32 maxsize, int32 rxsize)
 {
 	uint32 *p;
 	int32 i, ret, id;
 	uint32 port;
 	CodeMsg *c;

 	if((port = m->machport) == 0){
 		port = runtime·mach_reply_port();
 		m->machport = port;
 	}

 	h->msgh_bits |= MACH_MSGH_BITS(MACH_MSG_TYPE_COPY_SEND, MACH_MSG_TYPE_MAKE_SEND_ONCE);
 	h->msgh_local_port = port;
 	h->msgh_reserved = 0;
 	id = h->msgh_id;

 	if(DebugMach){
 		p = (uint32*)h;
 		runtime·prints("send:\t");
 		for(i=0; i<h->msgh_size/sizeof(p[0]); i++){
 			runtime·prints(" ");
 			runtime·printpointer((void*)p[i]);
 			if(i%8 == 7)
 				runtime·prints("\n\t");
 		}
 		if(i%8)
 			runtime·prints("\n");
 	}

 	ret = mach_msg(h, MACH_SEND_MSG|MACH_RCV_MSG,
 		h->msgh_size, maxsize, port, 0, 0);
 	if(ret != 0){
 		if(DebugMach){
 			runtime·prints("mach_msg error ");
 			runtime·printint(ret);
 			runtime·prints("\n");
 		}
 		return ret;
 	}

 	if(DebugMach){
 		p = (uint32*)h;
 		runtime·prints("recv:\t");
 		for(i=0; i<h->msgh_size/sizeof(p[0]); i++){
 			runtime·prints(" ");
 			runtime·printpointer((void*)p[i]);
 			if(i%8 == 7)
 				runtime·prints("\n\t");
 		}
 		if(i%8)
 			runtime·prints("\n");
 	}

 	if(h->msgh_id != id+Reply){
 		if(DebugMach){
 			runtime·prints("mach_msg reply id mismatch ");
 			runtime·printint(h->msgh_id);
 			runtime·prints(" != ");
 			runtime·printint(id+Reply);
 			runtime·prints("\n");
 		}
 		return -303;	// MIG_REPLY_MISMATCH
 	}

 	// Look for a response giving the return value.
 	// Any call can send this back with an error,
 	// and some calls only have return values so they
 	// send it back on success too.  I don't quite see how
 	// you know it's one of these and not the full response
 	// format, so just look if the message is right.
 	c = (CodeMsg*)h;
 	if(h->msgh_size == sizeof(CodeMsg)
 	&& !(h->msgh_bits & MACH_MSGH_BITS_COMPLEX)){
 		if(DebugMach){
 			runtime·prints("mig result ");
 			runtime·printint(c->code);
 			runtime·prints("\n");
 		}
 		return c->code;
 	}

 	if(h->msgh_size != rxsize){
 		if(DebugMach){
 			runtime·prints("mach_msg reply size mismatch ");
 			runtime·printint(h->msgh_size);
 			runtime·prints(" != ");
 			runtime·printint(rxsize);
 			runtime·prints("\n");
 		}
 		return -307;	// MIG_ARRAY_TOO_LARGE
 	}

 	return 0;
 }


 // Semaphores!

 enum
 {
 	Tmach_semcreate = 3418,
 	Rmach_semcreate = Tmach_semcreate + Reply,

 	Tmach_semdestroy = 3419,
 	Rmach_semdestroy = Tmach_semdestroy + Reply,

 	// Mach calls that get interrupted by Unix signals
 	// return this error code.  We retry them.
 	KERN_ABORTED = 14,
 };

 typedef struct Tmach_semcreateMsg Tmach_semcreateMsg;
 typedef struct Rmach_semcreateMsg Rmach_semcreateMsg;
 typedef struct Tmach_semdestroyMsg Tmach_semdestroyMsg;
 // Rmach_semdestroyMsg = CodeMsg

 #pragma pack on
 struct Tmach_semcreateMsg
 {
 	MachHeader h;
 	MachNDR ndr;
 	int32 policy;
 	int32 value;
 };

 struct Rmach_semcreateMsg
 {
 	MachHeader h;
 	MachBody body;
 	MachPort semaphore;
 };

 struct Tmach_semdestroyMsg
 {
 	MachHeader h;
 	MachBody body;
 	MachPort semaphore;
 };
 #pragma pack off

 uint32
 runtime·mach_semcreate(void)
 {
 	union {
 		Tmach_semcreateMsg tx;
 		Rmach_semcreateMsg rx;
 		uint8 pad[MinMachMsg];
 	} m;
 	int32 r;

 	m.tx.h.msgh_bits = 0;
 	m.tx.h.msgh_size = sizeof(m.tx);
 	m.tx.h.msgh_remote_port = runtime·mach_task_self();
 	m.tx.h.msgh_id = Tmach_semcreate;
 	m.tx.ndr = zerondr;

 	m.tx.policy = 0;	// 0 = SYNC_POLICY_FIFO
 	m.tx.value = 0;

 	while((r = machcall(&m.tx.h, sizeof m, sizeof(m.rx))) != 0){
 		if(r == KERN_ABORTED)	// interrupted
 			continue;
 		macherror(r, "semaphore_create");
 	}
 	if(m.rx.body.msgh_descriptor_count != 1)
 		unimplemented("mach_semcreate desc count");
 	return m.rx.semaphore.name;
 }

 void
 runtime·mach_semdestroy(uint32 sem)
 {
 	union {
 		Tmach_semdestroyMsg tx;
 		uint8 pad[MinMachMsg];
 	} m;
 	int32 r;

 	m.tx.h.msgh_bits = MACH_MSGH_BITS_COMPLEX;
 	m.tx.h.msgh_size = sizeof(m.tx);
 	m.tx.h.msgh_remote_port = runtime·mach_task_self();
 	m.tx.h.msgh_id = Tmach_semdestroy;
 	m.tx.body.msgh_descriptor_count = 1;
 	m.tx.semaphore.name = sem;
 	m.tx.semaphore.disposition = MACH_MSG_TYPE_MOVE_SEND;
 	m.tx.semaphore.type = 0;

 	while((r = machcall(&m.tx.h, sizeof m, 0)) != 0){
 		if(r == KERN_ABORTED)	// interrupted
 			continue;
 		macherror(r, "semaphore_destroy");
 	}
 }

 // The other calls have simple system call traps in sys.s
 int32 runtime·mach_semaphore_wait(uint32 sema);
 int32 runtime·mach_semaphore_timedwait(uint32 sema, uint32 sec, uint32 nsec);
 int32 runtime·mach_semaphore_signal(uint32 sema);
 int32 runtime·mach_semaphore_signal_all(uint32 sema);

 void
 runtime·mach_semacquire(uint32 sem)
 {
 	int32 r;

 	while((r = runtime·mach_semaphore_wait(sem)) != 0) {
 		if(r == KERN_ABORTED)	// interrupted
 			continue;
 		macherror(r, "semaphore_wait");
 	}
 }

 void
 runtime·mach_semrelease(uint32 sem)
 {
 	int32 r;

 	while((r = runtime·mach_semaphore_signal(sem)) != 0) {
 		if(r == KERN_ABORTED)	// interrupted
 			continue;
 		macherror(r, "semaphore_signal");
 	}
 }

 void
 runtime·sigpanic(void)
 {
 	switch(g->sig) {
 	case SIGBUS:
 		if(g->sigcode0 == BUS_ADRERR && g->sigcode1 < 0x1000)
 			runtime·panicstring("invalid memory address or nil pointer dereference");
 		runtime·printf("unexpected fault address %p\n", g->sigcode1);
 		runtime·throw("fault");
 	case SIGSEGV:
 		if((g->sigcode0 == 0 || g->sigcode0 == SEGV_MAPERR || g->sigcode0 == SEGV_ACCERR) && g->sigcode1 < 0x1000)
 			runtime·panicstring("invalid memory address or nil pointer dereference");
 		runtime·printf("unexpected fault address %p\n", g->sigcode1);
 		runtime·throw("fault");
 	case SIGFPE:
 		switch(g->sigcode0) {
 		case FPE_INTDIV:
 			runtime·panicstring("integer divide by zero");
 		case FPE_INTOVF:
 			runtime·panicstring("integer overflow");
 		}
 		runtime·panicstring("floating point error");
 	}
 	runtime·panicstring(runtime·sigtab[g->sig].name);
 }

 // TODO(rsc): place holder to fix build.
 void
 runtime·osyield(void)
 {
 }
	// Copyright 2009 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	#include "runtime.h"
	#include "defs.h"
	#include "os.h"
	#include "stack.h"

	extern SigTab runtime·sigtab[];

	static void
	unimplemented(int8 *name)
	{
	runtime·prints(name);
	runtime·prints(" not implemented\n");
	(int32)1231 = 1231;
	}

	// Thread-safe allocation of a semaphore.
	// Psema points at a kernel semaphore key.
	// It starts out zero, meaning no semaphore.
	// Fill it in, being careful of others calling initsema
	// simultaneously.
	static void
	initsema(uint32 *psema)
	{
	uint32 sema;

	if(*psema != 0) // already have one
	return;

	sema = runtime·mach_semcreate();
	if(!runtime·cas(psema, 0, sema)){
	// Someone else filled it in. Use theirs.
	runtime·mach_semdestroy(sema);
	return;
	}
	}


	// Blocking locks.

	// Implement Locks, using semaphores.
	// l->key is the number of threads who want the lock.
	// In a race, one thread increments l->key from 0 to 1
	// and the others increment it from >0 to >1. The thread
	// who does the 0->1 increment gets the lock, and the
	// others wait on the semaphore. When the 0->1 thread
	// releases the lock by decrementing l->key, l->key will
	// be >0, so it will increment the semaphore to wake up
	// one of the others. This is the same algorithm used
	// in Plan 9's user-level locks.

	void
	runtime·lock(Lock *l)
	{
	if(m->locks < 0)
	runtime·throw("lock count");
	m->locks++;

	if(runtime·xadd(&l->key, 1) > 1) { // someone else has it; wait
	// Allocate semaphore if needed.
	if(l->sema == 0)
	initsema(&l->sema);
	runtime·mach_semacquire(l->sema);
	}
	}

	void
	runtime·unlock(Lock *l)
	{
	m->locks--;
	if(m->locks < 0)
	runtime·throw("lock count");

	if(runtime·xadd(&l->key, -1) > 0) { // someone else is waiting
	// Allocate semaphore if needed.
	if(l->sema == 0)
	initsema(&l->sema);
	runtime·mach_semrelease(l->sema);
	}
	}

	static void
	destroylock(Lock *l)
	{
	if(l->sema != 0) {
	runtime·mach_semdestroy(l->sema);
	l->sema = 0;
	}
	}

	// User-level semaphore implementation:
	// try to do the operations in user space on u,
	// but when it's time to block, fall back on the kernel semaphore k.
	// This is the same algorithm used in Plan 9.
	void
	runtime·usemacquire(Usema *s)
	{
	if((int32)runtime·xadd(&s->u, -1) < 0) {
	if(s->k == 0)
	initsema(&s->k);
	runtime·mach_semacquire(s->k);
	}
	}

	void
	runtime·usemrelease(Usema *s)
	{
	if((int32)runtime·xadd(&s->u, 1) <= 0) {
	if(s->k == 0)
	initsema(&s->k);
	runtime·mach_semrelease(s->k);
	}
	}


	// Event notifications.
	void
	runtime·noteclear(Note *n)
	{
	n->wakeup = 0;
	}

	void
	runtime·notesleep(Note *n)
	{
	while(!n->wakeup)
	runtime·usemacquire(&n->sema);
	}

	void
	runtime·notewakeup(Note *n)
	{
	n->wakeup = 1;
	runtime·usemrelease(&n->sema);
	}


	// BSD interface for threading.
	void
	runtime·osinit(void)
	{
	// Register our thread-creation callback (see {amd64,386}/sys.s)
	// but only if we're not using cgo. If we are using cgo we need
	// to let the C pthread libary install its own thread-creation callback.
	if(!runtime·iscgo)
	runtime·bsdthread_register();
	runtime·destroylock = destroylock;

	// Use sysctl to fetch hw.ncpu.
	uint32 mib[2];
	uint32 out;
	int32 ret;
	uintptr nout;

	mib[0] = 6;
	mib[1] = 3;
	nout = sizeof out;
	out = 0;
	ret = runtime·sysctl(mib, 2, (byte*)&out, &nout, nil, 0);
	if(ret >= 0)
	runtime·ncpu = out;
	}

	void
	runtime·goenvs(void)
	{
	runtime·goenvs_unix();
	}

	void
	runtime·newosproc(M m, G g, void stk, void (fn)(void))
	{
	int32 errno;

	m->tls[0] = m->id; // so 386 asm can find it
	if(0){
	runtime·printf("newosproc stk=%p m=%p g=%p fn=%p id=%d/%d ostk=%p\n",
	stk, m, g, fn, m->id, m->tls[0], &m);
	}
	if((errno = runtime·bsdthread_create(stk, m, g, fn)) < 0) {
	runtime·printf("runtime: failed to create new OS thread (have %d already; errno=%d)\n", runtime·mcount(), -errno);
	runtime·throw("runtime.newosproc");
	}
	}

	// Called to initialize a new m (including the bootstrap m).
	void
	runtime·minit(void)
	{
	// Initialize signal handling.
	m->gsignal = runtime·malg(32*1024); // OS X wants >=8K, Linux >=2K
	runtime·signalstack(m->gsignal->stackguard - StackGuard, 32*1024);
	}

	// Mach IPC, to get at semaphores
	// Definitions are in /usr/include/mach on a Mac.

	static void
	macherror(int32 r, int8 *fn)
	{
	runtime·printf("mach error %s: %d\n", fn, r);
	runtime·throw("mach error");
	}

	enum
	{
	DebugMach = 0
	};

	static MachNDR zerondr;

	#define MACH_MSGH_BITS(a, b) ((a) \| ((b)<<8))

	static int32
	mach_msg(MachHeader *h,
	int32 op,
	uint32 send_size,
	uint32 rcv_size,
	uint32 rcv_name,
	uint32 timeout,
	uint32 notify)
	{
	// TODO: Loop on interrupt.
	return runtime·mach_msg_trap(h, op, send_size, rcv_size, rcv_name, timeout, notify);
	}

	// Mach RPC (MIG)

	enum
	{
	MinMachMsg = 48,
	Reply = 100,
	};

	#pragma pack on
	typedef struct CodeMsg CodeMsg;
	struct CodeMsg
	{
	MachHeader h;
	MachNDR NDR;
	int32 code;
	};
	#pragma pack off

	static int32
	machcall(MachHeader *h, int32 maxsize, int32 rxsize)
	{
	uint32 *p;
	int32 i, ret, id;
	uint32 port;
	CodeMsg *c;

	if((port = m->machport) == 0){
	port = runtime·mach_reply_port();
	m->machport = port;
	}

	h->msgh_bits \|= MACH_MSGH_BITS(MACH_MSG_TYPE_COPY_SEND, MACH_MSG_TYPE_MAKE_SEND_ONCE);
	h->msgh_local_port = port;
	h->msgh_reserved = 0;
	id = h->msgh_id;

	if(DebugMach){
	p = (uint32*)h;
	runtime·prints("send:\t");
	for(i=0; i<h->msgh_size/sizeof(p[0]); i++){
	runtime·prints(" ");
	runtime·printpointer((void*)p[i]);
	if(i%8 == 7)
	runtime·prints("\n\t");
	}
	if(i%8)
	runtime·prints("\n");
	}

	ret = mach_msg(h, MACH_SEND_MSG\|MACH_RCV_MSG,
	h->msgh_size, maxsize, port, 0, 0);
	if(ret != 0){
	if(DebugMach){
	runtime·prints("mach_msg error ");
	runtime·printint(ret);
	runtime·prints("\n");
	}
	return ret;
	}

	if(DebugMach){
	p = (uint32*)h;
	runtime·prints("recv:\t");
	for(i=0; i<h->msgh_size/sizeof(p[0]); i++){
	runtime·prints(" ");
	runtime·printpointer((void*)p[i]);
	if(i%8 == 7)
	runtime·prints("\n\t");
	}
	if(i%8)
	runtime·prints("\n");
	}

	if(h->msgh_id != id+Reply){
	if(DebugMach){
	runtime·prints("mach_msg reply id mismatch ");
	runtime·printint(h->msgh_id);
	runtime·prints(" != ");
	runtime·printint(id+Reply);
	runtime·prints("\n");
	}
	return -303; // MIG_REPLY_MISMATCH
	}

	// Look for a response giving the return value.
	// Any call can send this back with an error,
	// and some calls only have return values so they
	// send it back on success too. I don't quite see how
	// you know it's one of these and not the full response
	// format, so just look if the message is right.
	c = (CodeMsg*)h;
	if(h->msgh_size == sizeof(CodeMsg)
	&& !(h->msgh_bits & MACH_MSGH_BITS_COMPLEX)){
	if(DebugMach){
	runtime·prints("mig result ");
	runtime·printint(c->code);
	runtime·prints("\n");
	}
	return c->code;
	}

	if(h->msgh_size != rxsize){
	if(DebugMach){
	runtime·prints("mach_msg reply size mismatch ");
	runtime·printint(h->msgh_size);
	runtime·prints(" != ");
	runtime·printint(rxsize);
	runtime·prints("\n");
	}
	return -307; // MIG_ARRAY_TOO_LARGE
	}

	return 0;
	}


	// Semaphores!

	enum
	{
	Tmach_semcreate = 3418,
	Rmach_semcreate = Tmach_semcreate + Reply,

	Tmach_semdestroy = 3419,
	Rmach_semdestroy = Tmach_semdestroy + Reply,

	// Mach calls that get interrupted by Unix signals
	// return this error code. We retry them.
	KERN_ABORTED = 14,
	};

	typedef struct Tmach_semcreateMsg Tmach_semcreateMsg;
	typedef struct Rmach_semcreateMsg Rmach_semcreateMsg;
	typedef struct Tmach_semdestroyMsg Tmach_semdestroyMsg;
	// Rmach_semdestroyMsg = CodeMsg

	#pragma pack on
	struct Tmach_semcreateMsg
	{
	MachHeader h;
	MachNDR ndr;
	int32 policy;
	int32 value;
	};

	struct Rmach_semcreateMsg
	{
	MachHeader h;
	MachBody body;
	MachPort semaphore;
	};

	struct Tmach_semdestroyMsg
	{
	MachHeader h;
	MachBody body;
	MachPort semaphore;
	};
	#pragma pack off

	uint32
	runtime·mach_semcreate(void)
	{
	union {
	Tmach_semcreateMsg tx;
	Rmach_semcreateMsg rx;
	uint8 pad[MinMachMsg];
	} m;
	int32 r;

	m.tx.h.msgh_bits = 0;
	m.tx.h.msgh_size = sizeof(m.tx);
	m.tx.h.msgh_remote_port = runtime·mach_task_self();
	m.tx.h.msgh_id = Tmach_semcreate;
	m.tx.ndr = zerondr;

	m.tx.policy = 0; // 0 = SYNC_POLICY_FIFO
	m.tx.value = 0;

	while((r = machcall(&m.tx.h, sizeof m, sizeof(m.rx))) != 0){
	if(r == KERN_ABORTED) // interrupted
	continue;
	macherror(r, "semaphore_create");
	}
	if(m.rx.body.msgh_descriptor_count != 1)
	unimplemented("mach_semcreate desc count");
	return m.rx.semaphore.name;
	}

	void
	runtime·mach_semdestroy(uint32 sem)
	{
	union {
	Tmach_semdestroyMsg tx;
	uint8 pad[MinMachMsg];
	} m;
	int32 r;

	m.tx.h.msgh_bits = MACH_MSGH_BITS_COMPLEX;
	m.tx.h.msgh_size = sizeof(m.tx);
	m.tx.h.msgh_remote_port = runtime·mach_task_self();
	m.tx.h.msgh_id = Tmach_semdestroy;
	m.tx.body.msgh_descriptor_count = 1;
	m.tx.semaphore.name = sem;
	m.tx.semaphore.disposition = MACH_MSG_TYPE_MOVE_SEND;
	m.tx.semaphore.type = 0;

	while((r = machcall(&m.tx.h, sizeof m, 0)) != 0){
	if(r == KERN_ABORTED) // interrupted
	continue;
	macherror(r, "semaphore_destroy");
	}
	}

	// The other calls have simple system call traps in sys.s
	int32 runtime·mach_semaphore_wait(uint32 sema);
	int32 runtime·mach_semaphore_timedwait(uint32 sema, uint32 sec, uint32 nsec);
	int32 runtime·mach_semaphore_signal(uint32 sema);
	int32 runtime·mach_semaphore_signal_all(uint32 sema);

	void
	runtime·mach_semacquire(uint32 sem)
	{
	int32 r;

	while((r = runtime·mach_semaphore_wait(sem)) != 0) {
	if(r == KERN_ABORTED) // interrupted
	continue;
	macherror(r, "semaphore_wait");
	}
	}

	void
	runtime·mach_semrelease(uint32 sem)
	{
	int32 r;

	while((r = runtime·mach_semaphore_signal(sem)) != 0) {
	if(r == KERN_ABORTED) // interrupted
	continue;
	macherror(r, "semaphore_signal");
	}
	}

	void
	runtime·sigpanic(void)
	{
	switch(g->sig) {
	case SIGBUS:
	if(g->sigcode0 == BUS_ADRERR && g->sigcode1 < 0x1000)
	runtime·panicstring("invalid memory address or nil pointer dereference");
	runtime·printf("unexpected fault address %p\n", g->sigcode1);
	runtime·throw("fault");
	case SIGSEGV:
	if((g->sigcode0 == 0 \|\| g->sigcode0 == SEGV_MAPERR \|\| g->sigcode0 == SEGV_ACCERR) && g->sigcode1 < 0x1000)
	runtime·panicstring("invalid memory address or nil pointer dereference");
	runtime·printf("unexpected fault address %p\n", g->sigcode1);
	runtime·throw("fault");
	case SIGFPE:
	switch(g->sigcode0) {
	case FPE_INTDIV:
	runtime·panicstring("integer divide by zero");
	case FPE_INTOVF:
	runtime·panicstring("integer overflow");
	}
	runtime·panicstring("floating point error");
	}
	runtime·panicstring(runtime·sigtab[g->sig].name);
	}

	// TODO(rsc): place holder to fix build.
	void
	runtime·osyield(void)
	{
	}