diff options
| -rw-r--r-- | src/base/spinlock_internal.cc | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/src/base/spinlock_internal.cc b/src/base/spinlock_internal.cc index b9fadde..172a637 100644 --- a/src/base/spinlock_internal.cc +++ b/src/base/spinlock_internal.cc @@ -80,6 +80,7 @@ int32 SpinLockWait(volatile Atomic32 *w, int n, static int SuggestedDelayNS(int loop) { // Weak pseudo-random number generator to get some spread between threads // when many are spinning. +#ifdef BASE_HAS_ATOMIC64 static base::subtle::Atomic64 rand; uint64 r = base::subtle::NoBarrier_Load(&rand); r = 0x5deece66dLL * r + 0xb; // numbers from nrand48() @@ -96,6 +97,24 @@ static int SuggestedDelayNS(int loop) { // The futex path multiplies this by 16, since we expect explicit wakeups // almost always on that path. return r >> (44 - (loop >> 3)); +#else + static Atomic32 rand; + uint32 r = base::subtle::NoBarrier_Load(&rand); + r = 0x343fd * r + 0x269ec3; // numbers from MSVC++ + base::subtle::NoBarrier_Store(&rand, r); + + r <<= 1; // 31-bit random number now in top 31-bits. + if (loop < 0 || loop > 32) { // limit loop to 0..32 + loop = 32; + } + // loop>>3 cannot exceed 4 because loop cannot exceed 32. + // Select top 20..24 bits of lower 31 bits, + // giving approximately 0ms to 16ms. + // Mean is exponential in loop for first 32 iterations, then 8ms. + // The futex path multiplies this by 16, since we expect explicit wakeups + // almost always on that path. + return r >> (12 - (loop >> 3)); +#endif } } // namespace internal |