mirror of
https://github.com/ceph/ceph-csi.git
synced 2024-11-30 10:10:21 +00:00
5b7b5f1e3a
This commit updates the go-ceph to latest release. More details about release at https://github.com/ceph/go-ceph/releases/tag/v0.10.0 Signed-off-by: Madhu Rajanna <madhupr007@gmail.com>
91 lines
3.8 KiB
Go
91 lines
3.8 KiB
Go
package cutil
|
|
|
|
import (
|
|
"sync"
|
|
"unsafe"
|
|
)
|
|
|
|
// PtrGuard respresents a guarded Go pointer (pointing to memory allocated by Go
|
|
// runtime) stored in C memory (allocated by C)
|
|
type PtrGuard struct {
|
|
// These mutexes will be used as binary semaphores for signalling events from
|
|
// one thread to another, which - in contrast to other languages like C++ - is
|
|
// possible in Go, that is a Mutex can be locked in one thread and unlocked in
|
|
// another.
|
|
stored, release sync.Mutex
|
|
released bool
|
|
}
|
|
|
|
// WARNING: using binary semaphores (mutexes) for signalling like this is quite
|
|
// a delicate task in order to avoid deadlocks or panics. Whenever changing the
|
|
// code logic, please review at least three times that there is no unexpected
|
|
// state possible. Usually the natural choice would be to use channels instead,
|
|
// but these can not easily passed to C code because of the pointer-to-pointer
|
|
// cgo rule, and would require the use of a Go object registry.
|
|
|
|
// NewPtrGuard writes the goPtr (pointing to Go memory) into C memory at the
|
|
// position cPtr, and returns a PtrGuard object.
|
|
func NewPtrGuard(cPtr CPtr, goPtr unsafe.Pointer) *PtrGuard {
|
|
var v PtrGuard
|
|
// Since the mutexes are used for signalling, they have to be initialized to
|
|
// locked state, so that following lock attempts will block.
|
|
v.release.Lock()
|
|
v.stored.Lock()
|
|
// Start a background go routine that lives until Release is called. This
|
|
// calls a special function that makes sure the garbage collector doesn't touch
|
|
// goPtr, stores it into C memory at position cPtr and then waits until it
|
|
// reveices the "release" signal, after which it nulls out the C memory at
|
|
// cPtr and then exits.
|
|
go func() {
|
|
storeUntilRelease(&v, (*CPtr)(cPtr), uintptr(goPtr))
|
|
}()
|
|
// Wait for the "stored" signal from the go routine when the Go pointer has
|
|
// been stored to the C memory. <--(1)
|
|
v.stored.Lock()
|
|
return &v
|
|
}
|
|
|
|
// Release removes the guarded Go pointer from the C memory by overwriting it
|
|
// with NULL.
|
|
func (v *PtrGuard) Release() {
|
|
if !v.released {
|
|
v.released = true
|
|
v.release.Unlock() // Send the "release" signal to the go routine. -->(2)
|
|
v.stored.Lock() // Wait for the second "stored" signal when the C memory
|
|
// has been nulled out. <--(3)
|
|
|
|
}
|
|
}
|
|
|
|
// The uintptrPtr() helper function below assumes that uintptr has the same size
|
|
// as a pointer, although in theory it could be larger. Therefore we use this
|
|
// constant expression to assert size equality as a safeguard at compile time.
|
|
// How it works: the difference of both sizes is converted into an 8 bit value
|
|
// and left-bit-shifted by 8. This always creates an overflow error at compile
|
|
// time, if the difference of the sizes is not 0.
|
|
const _ = uint8(unsafe.Sizeof(uintptr(0))-PtrSize) << 8 // size assert
|
|
func uintptrPtr(p *CPtr) *uintptr {
|
|
return (*uintptr)(unsafe.Pointer(p))
|
|
}
|
|
|
|
//go:uintptrescapes
|
|
|
|
// From https://golang.org/src/cmd/compile/internal/gc/lex.go:
|
|
// For the next function declared in the file any uintptr arguments may be
|
|
// pointer values converted to uintptr. This directive ensures that the
|
|
// referenced allocated object, if any, is retained and not moved until the call
|
|
// completes, even though from the types alone it would appear that the object
|
|
// is no longer needed during the call. The conversion to uintptr must appear in
|
|
// the argument list.
|
|
// Also see https://golang.org/cmd/compile/#hdr-Compiler_Directives
|
|
|
|
func storeUntilRelease(v *PtrGuard, cPtr *CPtr, goPtr uintptr) {
|
|
uip := uintptrPtr(cPtr)
|
|
*uip = goPtr // store Go pointer in C memory at c_ptr
|
|
v.stored.Unlock() // send "stored" signal to main thread -->(1)
|
|
v.release.Lock() // wait for "release" signal from main thread when
|
|
// Release() has been called. <--(2)
|
|
*uip = 0 // reset C memory to NULL
|
|
v.stored.Unlock() // send second "stored" signal to main thread -->(3)
|
|
}
|