main_init_done = make(chan bool)
if iscgo {
+ if _cgo_pthread_key_created == nil {
+ throw("_cgo_pthread_key_created missing")
+ }
+
if _cgo_thread_start == nil {
throw("_cgo_thread_start missing")
}
if _cgo_notify_runtime_init_done == nil {
throw("_cgo_notify_runtime_init_done missing")
}
+
+ // Set the x_crosscall2_ptr C function pointer variable point to crosscall2.
+ if set_crosscall2 == nil {
+ throw("set_crosscall2 missing")
+ }
+ set_crosscall2()
+
// Start the template thread in case we enter Go from
// a C-created thread and need to create a new thread.
startTemplateThread()
// pressed into service as the scheduling stack and current
// goroutine for the duration of the cgo callback.
//
-// When the callback is done with the m, it calls dropm to
-// put the m back on the list.
+// It calls dropm to put the m back on the list,
+// 1. when the callback is done with the m in non-pthread platforms,
+// 2. or when the C thread exiting on pthread platforms.
+//
+// The signal argument indicates whether we're called from a signal
+// handler.
//
//go:nosplit
-func needm() {
+func needm(signal bool) {
if (iscgo || GOOS == "windows") && !cgoHasExtraM {
// Can happen if C/C++ code calls Go from a global ctor.
// Can also happen on Windows if a global ctor uses a
osSetupTLS(mp)
// Install g (= m->g0) and set the stack bounds
- // to match the current stack. We don't actually know
+ // to match the current stack. If we don't actually know
// how big the stack is, like we don't know how big any
- // scheduling stack is, but we assume there's at least 32 kB,
- // which is more than enough for us.
+ // scheduling stack is, but we assume there's at least 32 kB.
+ // If we can get a more accurate stack bound from pthread,
+ // use that.
setg(mp.g0)
gp := getg()
gp.stack.hi = getcallersp() + 1024
gp.stack.lo = getcallersp() - 32*1024
+ if !signal && _cgo_getstackbound != nil {
+ // Don't adjust if called from the signal handler.
+ // We are on the signal stack, not the pthread stack.
+ // (We could get the stack bounds from sigaltstack, but
+ // we're getting out of the signal handler very soon
+ // anyway. Not worth it.)
+ asmcgocall(_cgo_getstackbound, unsafe.Pointer(gp))
+ }
gp.stackguard0 = gp.stack.lo + _StackGuard
+ // Should mark we are already in Go now.
+ // Otherwise, we may call needm again when we get a signal, before cgocallbackg1,
+ // which means the extram list may be empty, that will cause a deadlock.
+ mp.isExtraInC = false
+
// Initialize this thread to use the m.
asminit()
minit()
sched.ngsys.Add(-1)
}
+// Acquire an extra m and bind it to the C thread when a pthread key has been created.
+//
+//go:nosplit
+func needAndBindM() {
+ needm(false)
+
+ if _cgo_pthread_key_created != nil && *(*uintptr)(_cgo_pthread_key_created) != 0 {
+ cgoBindM()
+ }
+}
+
// newextram allocates m's and puts them on the extra list.
// It is called with a working local m, so that it can do things
// like call schedlock and allocate.
gp.m = mp
mp.curg = gp
mp.isextra = true
+ // mark we are in C by default.
+ mp.isExtraInC = true
mp.lockedInt++
mp.lockedg.set(gp)
gp.lockedm.set(mp)
unlockextra(mp)
}
+// dropm puts the current m back onto the extra list.
+//
+// 1. On systems without pthreads, like Windows
// dropm is called when a cgo callback has called needm but is now
// done with the callback and returning back into the non-Go thread.
-// It puts the current m back onto the extra list.
//
// The main expense here is the call to signalstack to release the
// m's signal stack, and then the call to needm on the next callback
// call. These should typically not be scheduling operations, just a few
// atomics, so the cost should be small.
//
-// TODO(rsc): An alternative would be to allocate a dummy pthread per-thread
-// variable using pthread_key_create. Unlike the pthread keys we already use
-// on OS X, this dummy key would never be read by Go code. It would exist
-// only so that we could register at thread-exit-time destructor.
-// That destructor would put the m back onto the extra list.
-// This is purely a performance optimization. The current version,
-// in which dropm happens on each cgo call, is still correct too.
-// We may have to keep the current version on systems with cgo
-// but without pthreads, like Windows.
+// 2. On systems with pthreads
+// dropm is called while a non-Go thread is exiting.
+// We allocate a pthread per-thread variable using pthread_key_create,
+// to register a thread-exit-time destructor.
+// And store the g into a thread-specific value associated with the pthread key,
+// when first return back to C.
+// So that the destructor would invoke dropm while the non-Go thread is exiting.
+// This is much faster since it avoids expensive signal-related syscalls.
+//
+// NOTE: this always runs without a P, so, nowritebarrierrec required.
+//
+//go:nowritebarrierrec
func dropm() {
// Clear m and g, and return m to the extra list.
// After the call to setg we can only call nosplit functions
msigrestore(sigmask)
}
+// bindm store the g0 of the current m into a thread-specific value.
+//
+// We allocate a pthread per-thread variable using pthread_key_create,
+// to register a thread-exit-time destructor.
+// We are here setting the thread-specific value of the pthread key, to enable the destructor.
+// So that the pthread_key_destructor would dropm while the C thread is exiting.
+//
+// And the saved g will be used in pthread_key_destructor,
+// since the g stored in the TLS by Go might be cleared in some platforms,
+// before the destructor invoked, so, we restore g by the stored g, before dropm.
+//
+// We store g0 instead of m, to make the assembly code simpler,
+// since we need to restore g0 in runtime.cgocallback.
+//
+// On systems without pthreads, like Windows, bindm shouldn't be used.
+//
+// NOTE: this always runs without a P, so, nowritebarrierrec required.
+//
+//go:nosplit
+//go:nowritebarrierrec
+func cgoBindM() {
+ if GOOS == "windows" || GOOS == "plan9" {
+ fatal("bindm in unexpected GOOS")
+ }
+ g := getg()
+ if g.m.g0 != g {
+ fatal("the current g is not g0")
+ }
+ if _cgo_bindm != nil {
+ asmcgocall(_cgo_bindm, unsafe.Pointer(g))
+ }
+}
+
// A helper function for EnsureDropM.
func getm() uintptr {
return uintptr(unsafe.Pointer(getg().m))