go/src/pkg/runtime/linux/thread.c

// 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 int32 proccount;

int32 runtime·open(uint8*, int32, int32);
int32 runtime·close(int32);
int32 runtime·read(int32, void*, int32);

// Linux futex.
//
//	futexsleep(uint32 *addr, uint32 val)
//	futexwakeup(uint32 *addr)
//
// Futexsleep atomically checks if *addr == val and if so, sleeps on addr.
// Futexwakeup wakes up threads sleeping on addr.
// Futexsleep is allowed to wake up spuriously.

enum
{
	MUTEX_UNLOCKED = 0,
	MUTEX_LOCKED = 1,
	MUTEX_SLEEPING = 2,

	ACTIVE_SPIN = 4,
	ACTIVE_SPIN_CNT = 30,
	PASSIVE_SPIN = 1,

	FUTEX_WAIT = 0,
	FUTEX_WAKE = 1,

	EINTR = 4,
	EAGAIN = 11,
};

// TODO(rsc): I tried using 1<<40 here but futex woke up (-ETIMEDOUT).
// I wonder if the timespec that gets to the kernel
// actually has two 32-bit numbers in it, so that
// a 64-bit 1<<40 ends up being 0 seconds,
// 1<<8 nanoseconds.
static Timespec longtime =
{
	1<<30,	// 34 years
	0
};

// Atomically,
//	if(*addr == val) sleep
// Might be woken up spuriously; that's allowed.
static void
futexsleep(uint32 *addr, uint32 val)
{
	// Some Linux kernels have a bug where futex of
	// FUTEX_WAIT returns an internal error code
	// as an errno.  Libpthread ignores the return value
	// here, and so can we: as it says a few lines up,
	// spurious wakeups are allowed.
	runtime·futex(addr, FUTEX_WAIT, val, &longtime, nil, 0);
}

// If any procs are sleeping on addr, wake up at most cnt.
static void
futexwakeup(uint32 *addr, uint32 cnt)
{
	int64 ret;

	ret = runtime·futex(addr, FUTEX_WAKE, cnt, nil, nil, 0);

	if(ret >= 0)
		return;

	// I don't know that futex wakeup can return
	// EAGAIN or EINTR, but if it does, it would be
	// safe to loop and call futex again.
	runtime·printf("futexwakeup addr=%p returned %D\n", addr, ret);
	*(int32*)0x1006 = 0x1006;
}

static int32
getproccount(void)
{
	int32 fd, rd, cnt, cpustrlen;
	byte *cpustr, *pos, *bufpos;
	byte buf[256];

	fd = runtime·open((byte*)"/proc/stat", O_RDONLY|O_CLOEXEC, 0);
	if(fd == -1)
		return 1;
	cnt = 0;
	bufpos = buf;
	cpustr = (byte*)"\ncpu";
	cpustrlen = runtime·findnull(cpustr);
	for(;;) {
		rd = runtime·read(fd, bufpos, sizeof(buf)-cpustrlen);
		if(rd == -1)
			break;
		bufpos[rd] = 0;
		for(pos=buf; pos=runtime·strstr(pos, cpustr); cnt++, pos++) {
		}
		if(rd < cpustrlen)
			break;
		runtime·memmove(buf, bufpos+rd-cpustrlen+1, cpustrlen-1);
		bufpos = buf+cpustrlen-1;
	}
	runtime·close(fd);
	return cnt ? cnt : 1;
}

// Possible lock states are MUTEX_UNLOCKED, MUTEX_LOCKED and MUTEX_SLEEPING.
// MUTEX_SLEEPING means that there is presumably at least one sleeping thread.
// Note that there can be spinning threads during all states - they do not
// affect mutex's state.
static void
futexlock(Lock *l)
{
	uint32 i, v, wait, spin;

	// Speculative grab for lock.
	v = runtime·xchg(&l->key, MUTEX_LOCKED);
	if(v == MUTEX_UNLOCKED)
		return;

	// wait is either MUTEX_LOCKED or MUTEX_SLEEPING
	// depending on whether there is a thread sleeping
	// on this mutex.  If we ever change l->key from
	// MUTEX_SLEEPING to some other value, we must be
	// careful to change it back to MUTEX_SLEEPING before
	// returning, to ensure that the sleeping thread gets
	// its wakeup call.
	wait = v;

	if(proccount == 0)
		proccount = getproccount();

	// On uniprocessor's, no point spinning.
	// On multiprocessors, spin for ACTIVE_SPIN attempts.
	spin = 0;
	if(proccount > 1)
		spin = ACTIVE_SPIN;

	for(;;) {
		// Try for lock, spinning.
		for(i = 0; i < spin; i++) {
			while(l->key == MUTEX_UNLOCKED)
				if(runtime·cas(&l->key, MUTEX_UNLOCKED, wait))
						return;
			runtime·procyield(ACTIVE_SPIN_CNT);
		}

		// Try for lock, rescheduling.
		for(i=0; i < PASSIVE_SPIN; i++) {
			while(l->key == MUTEX_UNLOCKED)
				if(runtime·cas(&l->key, MUTEX_UNLOCKED, wait))
					return;
			runtime·osyield();
		}

		// Sleep.
		v = runtime·xchg(&l->key, MUTEX_SLEEPING);
		if(v == MUTEX_UNLOCKED)
			return;
		wait = MUTEX_SLEEPING;
		futexsleep(&l->key, MUTEX_SLEEPING);
	}
}

static void
futexunlock(Lock *l)
{
	uint32 v;

	v = runtime·xchg(&l->key, MUTEX_UNLOCKED);
	if(v == MUTEX_UNLOCKED)
		runtime·throw("unlock of unlocked lock");
	if(v == MUTEX_SLEEPING)
		futexwakeup(&l->key, 1);
}

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

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


// One-time notifications.
void
runtime·noteclear(Note *n)
{
	n->state = 0;
}

void
runtime·notewakeup(Note *n)
{
	runtime·xchg(&n->state, 1);
	futexwakeup(&n->state, 1<<30);
}

void
runtime·notesleep(Note *n)
{
	while(runtime·atomicload(&n->state) == 0)
		futexsleep(&n->state, 0);
}


// Clone, the Linux rfork.
enum
{
	CLONE_VM = 0x100,
	CLONE_FS = 0x200,
	CLONE_FILES = 0x400,
	CLONE_SIGHAND = 0x800,
	CLONE_PTRACE = 0x2000,
	CLONE_VFORK = 0x4000,
	CLONE_PARENT = 0x8000,
	CLONE_THREAD = 0x10000,
	CLONE_NEWNS = 0x20000,
	CLONE_SYSVSEM = 0x40000,
	CLONE_SETTLS = 0x80000,
	CLONE_PARENT_SETTID = 0x100000,
	CLONE_CHILD_CLEARTID = 0x200000,
	CLONE_UNTRACED = 0x800000,
	CLONE_CHILD_SETTID = 0x1000000,
	CLONE_STOPPED = 0x2000000,
	CLONE_NEWUTS = 0x4000000,
	CLONE_NEWIPC = 0x8000000,
};

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

	/*
	 * note: strace gets confused if we use CLONE_PTRACE here.
	 */
	flags = CLONE_VM	/* share memory */
		| CLONE_FS	/* share cwd, etc */
		| CLONE_FILES	/* share fd table */
		| CLONE_SIGHAND	/* share sig handler table */
		| CLONE_THREAD	/* revisit - okay for now */
		;

	m->tls[0] = m->id;	// so 386 asm can find it
	if(0){
		runtime·printf("newosproc stk=%p m=%p g=%p fn=%p clone=%p id=%d/%d ostk=%p\n",
			stk, m, g, fn, runtime·clone, m->id, m->tls[0], &m);
	}

	if((ret = runtime·clone(flags, stk, m, g, fn)) < 0) {
		runtime·printf("runtime: failed to create new OS thread (have %d already; errno=%d)\n", runtime·mcount(), -ret);
		runtime·throw("runtime.newosproc");
	}
}

void
runtime·osinit(void)
{
}

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

// 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);
}

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);
}