[英]How to protect a non-atomic variable from modification by both interrupt and application code without blocking
我希望能夠在不阻塞的情況下修改中斷上下文或應用程序上下文中的非原子變量。 為了防止 ISR 阻塞,我使用原子標志來保護非原子數據。
#include <atomic>
#include <cstdint>
using CountLock = std::atomic<bool>;
static_assert(CountLock::is_always_lock_free, "count lock must be lock free");
#define TARGET_COUNT (1000)
CountLock count_locked{false};
uint64_t count{0}; // non-atomic on 32-bit system
// In interrupt
void MyISR()
{
// Don't modify count if locked
if (count_locked)
return;
++count; // non-atomic
if (count == TARGET_COUNT)
// Do something
}
// Application code (not in interrupt)
void setCount(uint64_t newCount)
{
// lock count while we are setting it
count_locked = true;
count = newCount;
count_locked = false;
}
考慮兩個線程同時分別調用MyISR
和setCount
:
T1 T2
if (count_locked)
return;
count_locked = true;
++count; /*non-atomic*/ count = newCount; // << data race
if (count == TARGET_COUNT)
// Do something
count_locked = false;
原子不保護對count
寫入。
不
數據被修改而沒有被正確鎖定
是的。 引用何時在多線程中使用 volatile? :“對於平台無關的多線程應用程序編程,易失性(幾乎)是無用的。”
不
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