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use std::sync::{ Arc, Mutex, Condvar};
// LockState can be in several possible states:
// 1. 0 readers, false upgradeable_reader, false writer. No-one has any locks, anyone can acquire anything (initial state)
// 2. 1+ readers, false upgradeable_reader, false writer - readers. writer cannot be acquired, but upgradeable_reader can be
// 3. 1+ readers, true upgradeable_reader, false writer - bunch of readers, and one thread that could upgrade to writer, but not yet
// 4. 0 readers, true upgradeable_reader, false writer - upgradeable_reader thread can upgrade to writer
// 5. 0 readers, false upgradeable_reader, true writer - writer only. Nothing else can be acquired.
struct LockState {
readers: u32,
upgradeable_reader: bool,
writer: bool
}
struct Locks(Arc<(Mutex<LockState>, Condvar)>);
impl Locks {
pub fn new() -> Locks {
Locks(Arc::new((Mutex::new(
LockState {
readers: 0,
upgradeable_reader: false,
writer: false
}), Condvar::new())))
}
pub fn read() ->
}
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