From 72bffb0807925a156b076b71f78c848a08d27b87 Mon Sep 17 00:00:00 2001
From: lichao <lichao@aiotlink.com>
Date: 星期四, 29 四月 2021 10:55:35 +0800
Subject: [PATCH] refactor mutex.
---
src/robust.h | 73 +++++++++++++++++++++++-------------
1 files changed, 47 insertions(+), 26 deletions(-)
diff --git a/src/robust.h b/src/robust.h
index 19e9bda..983567f 100644
--- a/src/robust.h
+++ b/src/robust.h
@@ -32,6 +32,7 @@
using namespace std::chrono;
using namespace std::chrono_literals;
+constexpr uint64_t MaskBits(int nbits) { return (uint64_t(1) << nbits) - 1; }
void QuickSleep();
@@ -102,20 +103,41 @@
char buf[4];
};
-template <bool isRobust = false>
-class CasMutex
+class PidLocker
{
- static pid_t pid()
+public:
+ typedef int locker_t;
+ static locker_t this_locker()
{
- static pid_t val = getpid();
+ static locker_t val = getpid();
return val;
}
- static bool Killed(pid_t pid)
+ static bool is_alive(locker_t locker) { return true; }
+};
+
+class RobustPidLocker
+{
+public:
+ typedef int locker_t;
+ static locker_t this_locker()
+ {
+ static locker_t val = getpid();
+ return val;
+ }
+ static bool is_alive(locker_t locker)
{
char buf[64] = {0};
- snprintf(buf, sizeof(buf) - 1, "/proc/%d/stat", pid);
- return access(buf, F_OK) != 0;
+ snprintf(buf, sizeof(buf) - 1, "/proc/%d/stat", locker);
+ return access(buf, F_OK) == 0;
}
+};
+
+template <class LockerT>
+class CasMutex
+{
+ typedef typename LockerT::locker_t locker_t;
+ static inline locker_t this_locker() { return LockerT::this_locker(); }
+ static inline bool is_alive(locker_t locker) { return LockerT::is_alive(locker); }
public:
CasMutex() :
@@ -126,11 +148,11 @@
auto old = meta_.load();
int r = 0;
if (!Locked(old)) {
- r = MetaCas(old, Meta(1, pid()));
- } else if (isRobust && Killed(Pid(old))) {
- r = static_cast<int>(MetaCas(old, Meta(1, pid()))) << 1;
+ r = MetaCas(old, Meta(1, this_locker()));
+ } else if (!is_alive(Locker(old))) {
+ r = static_cast<int>(MetaCas(old, Meta(1, this_locker()))) << 1;
if (r) {
- printf("captured pid %d -> %d, r = %d\n", Pid(old), pid(), r);
+ printf("captured pid %d -> %d, r = %d\n", Locker(old), this_locker(), r);
}
}
return r;
@@ -146,19 +168,21 @@
void unlock()
{
auto old = meta_.load();
- if (Locked(old) && Pid(old) == pid()) {
- MetaCas(old, Meta(0, pid()));
+ if (Locked(old) && Locker(old) == this_locker()) {
+ MetaCas(old, Meta(0, this_locker()));
}
}
private:
+ static_assert(sizeof(locker_t) < sizeof(uint64_t), "locker size must be smaller than 64 bit!");
std::atomic<uint64_t> meta_;
bool Locked(uint64_t meta) { return (meta >> 63) != 0; }
- pid_t Pid(uint64_t meta) { return meta & ~(uint64_t(1) << 63); }
- uint64_t Meta(uint64_t lk, pid_t pid) { return (lk << 63) | pid; }
+ locker_t Locker(uint64_t meta) { return meta & MaskBits(sizeof(locker_t) * 8); }
+ uint64_t Meta(uint64_t lk, locker_t lid) { return (lk << 63) | lid; }
bool MetaCas(uint64_t exp, uint64_t val) { return meta_.compare_exchange_strong(exp, val); }
- static_assert(sizeof(pid_t) < sizeof(uint64_t));
};
+
+typedef CasMutex<RobustPidLocker> Mutex;
template <class Lock>
class Guard
@@ -193,19 +217,17 @@
state_(0), capacity_(cap), mhead_(0), mtail_(0), al_(al), buf(al_.allocate(cap))
{
if (!buf) {
- throw("error allocate buffer: out of mem!");
+ throw("robust CircularBuffer allocate error: alloc buffer failed, out of mem!");
}
}
- ~CircularBuffer()
- {
- al_.deallocate(buf, capacity_);
- }
+ ~CircularBuffer() { al_.deallocate(buf, capacity_); }
+
size_type size() const { return (capacity_ + tail() - head()) % capacity_; }
bool full() const { return (capacity_ + tail() + 1 - head()) % capacity_ == 0; }
bool empty() const { return head() == tail(); }
bool push_back(Data d)
{
- Guard<MutexT> guard(mutex_);
+ Guard<Mutex> guard(mutex_);
if (!full()) {
auto old = mtail();
buf[Pos(old)] = d;
@@ -216,7 +238,7 @@
}
bool pop_front(Data &d)
{
- Guard<MutexT> guard(mutex_);
+ Guard<Mutex> guard(mutex_);
if (!empty()) {
auto old = mhead();
d = buf[Pos(old)];
@@ -233,8 +255,7 @@
CircularBuffer(CircularBuffer &&);
CircularBuffer &operator=(const CircularBuffer &) = delete;
CircularBuffer &operator=(CircularBuffer &&) = delete;
- typedef CasMutex<true> MutexT;
- // static_assert(sizeof(MutexT) == 16);
+
meta_type next(meta_type meta) const { return Meta(Count(meta) + 1, (Pos(meta) + 1) % capacity_); }
size_type head() const { return Pos(mhead()); }
size_type tail() const { return Pos(mtail()); }
@@ -244,7 +265,7 @@
enum { eStateReady = 0x19833891 };
std::atomic<uint32_t> state_;
const size_type capacity_;
- MutexT mutex_;
+ Mutex mutex_;
std::atomic<meta_type> mhead_;
std::atomic<meta_type> mtail_;
Alloc al_;
--
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