私はたまたま Queued Spinlock に出くわし、C++ で実装したいと考えています。これに関する情報を少しグーグルで検索しましたが、適切なドキュメントを取得できませんでした。
ドキュメント/実装のヒントは大歓迎です。
前もって感謝します
マイケル・ブラウンが指摘したコードには、次の疑問があります
// represents processor in wait queue of the spinlock
struct qsl_entry
{
// next processor in the queue that is waiting to enter section
qsl_entry* next;
// indicates whether the access to section has been granted to processor
int state;
};
// queued spinlock
struct qsl
{
// the first processor in the queue that is waiting to enter section
qsl_entry* head;
};
// requests access to critical section guarded by the spinlock,
// if the section is already taken it puts processor to wait
// and insert it into queue
// lck - queued lock that used to guard section
// ent - entry that represent processor in queue of the spinlock
void lock_qsl(qsl* lck, qsl_entry* ent)
{
__asm
{
mov eax, ent;
mov ebx, lck;
// prepare queue entry
mov [eax], 0;
mov edx, eax;
mov [eax]qsl_entry.state, 1;
// store it as the last entry of the queue -- Is this what is line is doing ?
// ebx contains address of lck & [ ebx ] refers to address pointed by lck &
// it is over written to ent. eax now contains the memory the lck was pointing to.
lock xchg [ebx],eax;
// if the section available grant access to processor?
test eax, eax;
jz enter_section;
// link new entry with the rest of queue -- really ? are we nt overwritting
// the next pointer here ?
mov [eax],edx
// wait for processor's turn
wait1:
pause;
cmp [edx]qsl_entry.state, 1;
je wait1;
enter_section:
}
}
この実装は正しいですか? 私はそうは思わない！