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use weaker atomic operations

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(havent noticed a performance improvement. but it's nice having it correct)
This commit is contained in:
Desour 2024-10-05 09:17:13 +02:00
parent 668d22f39f
commit 76b5d120e8
1 changed files with 11 additions and 6 deletions
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17
src/threading/ipc_channel.cpp
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@ -119,8 +119,13 @@ static bool wait(IPCChannelBuffer *buf, const struct timespec *timeout) noexcept
// try busy waiting // try busy waiting
for (int i = 0; i < 100; i++) { for (int i = 0; i < 100; i++) {
// posted? // posted?
if (buf->futex.exchange(0) == 1) if (buf->futex.load(std::memory_order_acquire) == 1) {
return true; // yes // yes
// reset it. (relaxed ordering is sufficient, because the other thread
// does not need to see the side effects we did before writing 0)
buf->futex.store(0, std::memory_order_relaxed);
return true;
}
#if defined(__i386__) || defined(__x86_64__) #if defined(__i386__) || defined(__x86_64__)
busy_wait(40); busy_wait(40);
#else #else
@ -130,9 +135,9 @@ static bool wait(IPCChannelBuffer *buf, const struct timespec *timeout) noexcept
// wait with futex // wait with futex
while (true) { while (true) {
// write 2 to show that we're futexing // write 2 to show that we're futexing
if (buf->futex.exchange(2) == 1) { if (buf->futex.exchange(2, std::memory_order_acq_rel) == 1) {
// futex was posted => change 2 to 0 (or 1 to 1) // it was posted in the meantime
buf->futex.fetch_and(1); buf->futex.store(0, std::memory_order_relaxed);
return true; return true;
} }
int s = futex(&buf->futex, FUTEX_WAIT, 2, timeout, nullptr, 0); int s = futex(&buf->futex, FUTEX_WAIT, 2, timeout, nullptr, 0);
@ -164,7 +169,7 @@ static bool wait(IPCChannelBuffer *buf, const struct timespec *timeout) noexcept
static void post(IPCChannelBuffer *buf) noexcept static void post(IPCChannelBuffer *buf) noexcept
{ {
#if defined(IPC_CHANNEL_IMPLEMENTATION_LINUX_FUTEX) #if defined(IPC_CHANNEL_IMPLEMENTATION_LINUX_FUTEX)
if (buf->futex.exchange(1) == 2) { if (buf->futex.exchange(1, std::memory_order_acq_rel) == 2) {
// 2 means reader needs to be notified // 2 means reader needs to be notified
int s = futex(&buf->futex, FUTEX_WAKE, 1, nullptr, nullptr, 0); int s = futex(&buf->futex, FUTEX_WAKE, 1, nullptr, nullptr, 0);
if (s == -1) { if (s == -1) {