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Original file line number | Diff line number | Diff line change |
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#include "msgq/futex.h" | ||
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#include <fcntl.h> | ||
#include <limits.h> | ||
#include <linux/futex.h> | ||
#include <stdio.h> | ||
#include <sys/mman.h> | ||
#include <syscall.h> | ||
#include <unistd.h> | ||
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#include <cassert> | ||
#include <stdexcept> | ||
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Futex::Futex(const std::string &path) { | ||
auto fd = open(path.c_str(), O_RDWR | O_CREAT, 0664); | ||
if (fd < 0) { | ||
throw std::runtime_error("Failed to open file: " + path); | ||
} | ||
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if (ftruncate(fd, sizeof(uint32_t)) < 0) { | ||
close(fd); | ||
throw std::runtime_error("Failed to truncate file: " + path); | ||
} | ||
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int *mem = (int *)mmap(NULL, sizeof(uint32_t), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); | ||
close(fd); | ||
if (mem == MAP_FAILED) { | ||
throw std::runtime_error("Failed to mmap file: " + path); | ||
} | ||
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futex = reinterpret_cast<std::atomic<uint32_t> *>(mem); | ||
} | ||
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Futex::~Futex() { | ||
munmap(futex, sizeof(uint32_t)); | ||
} | ||
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void Futex::broadcast() { | ||
// Increment the futex value to signal waiting threads | ||
futex->fetch_add(1, std::memory_order_relaxed); | ||
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// Wake up all threads waiting on the futex | ||
syscall(SYS_futex, futex, FUTEX_WAKE, INT_MAX, NULL, NULL, 0); | ||
} | ||
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bool Futex::wait(uint32_t expected, int timeout_ms) { | ||
if (futex->load(std::memory_order_relaxed) != expected) { | ||
return true; // Already not equal, no need to wait | ||
} | ||
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if (timeout_ms <= 0) { | ||
return false; // Timeout immediately | ||
} | ||
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// Perform the futex wait syscall | ||
struct timespec ts; | ||
ts.tv_sec = timeout_ms / 1000; | ||
ts.tv_nsec = (timeout_ms % 1000) * 1000 * 1000; | ||
syscall(SYS_futex, futex, FUTEX_WAIT, expected, &ts, nullptr, 0); | ||
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return futex->load(std::memory_order_relaxed) != expected; | ||
} |
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#pragma once | ||
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#include <cstdint> | ||
#include <atomic> | ||
#include <string> | ||
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class Futex { | ||
public: | ||
Futex(const std::string &path); | ||
~Futex(); | ||
void broadcast(); | ||
bool wait(uint32_t expected, int timeout_ms); | ||
inline uint32_t value() const { return futex->load(); } | ||
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private: | ||
std::atomic<uint32_t> *futex = nullptr; | ||
}; |
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