cds/misc/rwlock.h

   1 #ifndef _RWLOCK_H
   2 #define _RWLOCK_H
   3
   4 #include "backoff.h"
   5 #include <atomic>
   6 #include <cds/algo/backoff_strategy.h>
   7 #include <thread>
   8
   9 namespace cds_others {
  10
  11 #define RW_LOCK_BIAS 0x00100000
  12 #define WRITE_LOCK_CMP RW_LOCK_BIAS
  13
  14 using std::memory_order_acquire;
  15 using std::memory_order_release;
  16 using std::memory_order_relaxed;
  17 using std::atomic_int;
  18
  19 class RWLock {
  20 public:
  21   RWLock() {
  22     lock.store(RW_LOCK_BIAS);
  23   }
  24
  25   int read_can_lock() {
  26     return atomic_load_explicit(&lock, memory_order_relaxed) > 0;
  27   }
  28
  29   int write_can_lock() {
  30     return atomic_load_explicit(&lock, memory_order_relaxed) == RW_LOCK_BIAS;
  31   }
  32
  33   void read_lock() {
  34     ExpBackoff backoff;
  35     int priorvalue = atomic_fetch_sub_explicit(&lock, 1, memory_order_acquire);
  36     while (priorvalue <= 0) {
  37       atomic_fetch_add_explicit(&lock, 1, memory_order_relaxed);
  38       while (atomic_load_explicit(&lock, memory_order_relaxed) <= 0) {
  39         backoff();
  40       }
  41       priorvalue = atomic_fetch_sub_explicit(&lock, 1, memory_order_acquire);
  42     }
  43   }
  44
  45   void write_lock() {
  46     int priorvalue =
  47         atomic_fetch_sub_explicit(&lock, RW_LOCK_BIAS, memory_order_acquire);
  48     ExpBackoff backoff;
  49     while (priorvalue != RW_LOCK_BIAS) {
  50       atomic_fetch_add_explicit(&lock, RW_LOCK_BIAS, memory_order_relaxed);
  51       while (atomic_load_explicit(&lock, memory_order_relaxed) !=
  52              RW_LOCK_BIAS) {
  53         backoff();
  54       }
  55       priorvalue =
  56           atomic_fetch_sub_explicit(&lock, RW_LOCK_BIAS, memory_order_acquire);
  57     }
  58   }
  59
  60   int read_trylock() {
  61     int priorvalue = atomic_fetch_sub_explicit(&lock, 1, memory_order_acquire);
  62     if (priorvalue > 0)
  63       return 1;
  64
  65     atomic_fetch_add_explicit(&lock, 1, memory_order_relaxed);
  66     return 0;
  67   }
  68
  69   int write_trylock() {
  70     int priorvalue =
  71         atomic_fetch_sub_explicit(&lock, RW_LOCK_BIAS, memory_order_acquire);
  72     if (priorvalue == RW_LOCK_BIAS)
  73       return 1;
  74
  75     atomic_fetch_add_explicit(&lock, RW_LOCK_BIAS, memory_order_relaxed);
  76     return 0;
  77   }
  78
  79   void read_unlock() {
  80     atomic_fetch_add_explicit(&lock, 1, memory_order_release);
  81   }
  82
  83   void write_unlock() {
  84     atomic_fetch_add_explicit(&lock, RW_LOCK_BIAS, memory_order_release);
  85   }
  86
  87 private:
  88   atomic_int lock;
  89 };
  90
  91 } // namespace cds_others
  92
  93 #endif