rwlock.h

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#pragma once
 
#include <cx/cx.h>
#include <cx/meta/block.h>
#include <cx/platform/base.h>
#include "aspin.h"
#include "futex.h"
 
#ifdef CX_LOCK_DEBUG
#include <cx/log/log.h>
#endif
 
CX_C_BEGIN
 
enum RWLOCK_Flags {
    RWLOCK_NoSpin = 1,   
};
 
#define RWLOCK_READER_MAX   4095
#define RWLOCK_READWAIT_MAX 2047
#define RWLOCK_WRITER_MAX   511
 
#define RWLOCK_READER_MASK     (0x00000fff)
#define RWLOCK_READWAIT_MASK   (0x007ff000)
#define RWLOCK_WRITER_MASK     (0xff800000)
#define RWLOCK_READERS(state)  ((state) & RWLOCK_READER_MASK)
#define RWLOCK_READWAIT(state) (((state) & RWLOCK_READWAIT_MASK) >> 12)
#define RWLOCK_WRITERS(state)  (((state) & RWLOCK_WRITER_MASK) >> 23)
#define RWLOCK_READ_ADD        0x00000001
#define RWLOCK_READWAIT_ADD    0x00001000
#define RWLOCK_WRITE_ADD       0x00800000
 
typedef struct RWLock {
    atomic(uint32) state;   
    Futex rftx;             
    Futex wftx;             
    AdaptiveSpin aspin;     
} RWLock;
 
void _rwlockInit(_Out_ RWLock* l, uint32 flags);
 
#define rwlockInit(l, ...) _rwlockInit(l, opt_flags(__VA_ARGS__))
 
_When_(return == true, _Acquires_shared_lock_(*l)) _When_(timeout == timeForever, _Acquires_shared_lock_(*l)) _When_(timeout != timeForever, _Must_inspect_result_) bool rwlockTryAcquireReadTimeout(_Inout_ RWLock* l, int64 timeout);
 
_When_(return == true, _Acquires_exclusive_lock_(*l)) _When_(timeout == timeForever, _Acquires_exclusive_lock_(*l)) _When_(timeout != timeForever, _Must_inspect_result_) bool rwlockTryAcquireWriteTimeout(_Inout_ RWLock* l, int64 timeout);
 
_When_(return == true, _Acquires_shared_lock_(*l)) _Must_inspect_result_ _meta_inline bool rwlockTryAcquireRead(_Inout_ RWLock* l)
{
    uint32 state = atomicLoad(uint32, &l->state, Relaxed);
    // only valid when no writer locks are held or pending
    if (RWLOCK_WRITERS(state) == 0) {
        // cannot acquire if we are at the max
        if (RWLOCK_READERS(state) == RWLOCK_READER_MAX)
            return false;
        if (atomicCompareExchange(uint32,
                                  strong,
                                  &l->state,
                                  &state,
                                  state + RWLOCK_READ_ADD,
                                  Acquire,
                                  Relaxed)) {
            aspinRecordUncontended(&l->aspin);
            return true;   // got the lock
        }
    }
 
    // no longer have valid conditions in which this lock can be acquired
    return false;
}
 
_When_(return == true, _Acquires_exclusive_lock_(*l)) _Must_inspect_result_ _meta_inline bool rwlockTryAcquireWrite(_Inout_ RWLock* l)
{
    uint32 state = atomicLoad(uint32, &l->state, Relaxed);
    // only valid when no other writer locks are held, and there are no (active) readers
    if (RWLOCK_WRITERS(state) == 0 && RWLOCK_READERS(state) == 0) {
        // make sure we didn't hit the limit
        if (RWLOCK_WRITERS(state) == RWLOCK_WRITER_MAX)
            return false;
        if (atomicCompareExchange(uint32,
                                  strong,
                                  &l->state,
                                  &state,
                                  state + RWLOCK_WRITE_ADD,
                                  Acquire,
                                  Relaxed)) {
            aspinRecordUncontended(&l->aspin);
            return true;   // got the lock
        }
    }
 
    // no longer have valid conditions in which this lock can be acquired
    return false;
}
 
_Acquires_shared_lock_(*l) _meta_inline void rwlockAcquireRead(_Inout_ RWLock* l)
{
    if (!rwlockTryAcquireReadTimeout(l, timeForever))
        relFatalError("Failed to acquire read lock (too many waiting readers?)");
}
 
#define withReadLock(l) blkWrap (rwlockAcquireRead(l), rwlockReleaseRead(l))
 
#define withWriteLock(l) blkWrap (rwlockAcquireWrite(l), rwlockReleaseWrite(l))
 
#ifdef CX_LOCK_DEBUG
// see the note on _logFmtMutexArgComp in mutex.h
#define _logFmtRwlockArgComp(level, fmt, ...) \
    _logFmtArgs(level, LogDefault, LOG_SiteAlways, 0, fmt, __VA_ARGS__)
_Acquires_shared_lock_(*l)
    static bool rwlockLogAndAcquireRead(_Inout_ RWLock* l, const char* name,
                                        const char* filename, int line)
{
    _logFmtRwlockArgComp(CX_LOCK_DEBUG,
                         _S"Locking rwlock ${string} for READ at ${string}:${int}",
                         stvar(string, (string)name),
                         stvar(string, (string)filename),
                         stvar(int32, line));
    rwlockAcquireRead(l);
    return true;
}
 
#define rwlockAcquireRead(l) rwlockLogAndAcquireRead(l, #l, __FILE__, __LINE__)
#endif
 
_Acquires_exclusive_lock_(*l) _meta_inline void rwlockAcquireWrite(_Inout_ RWLock* l)
{
    if (!rwlockTryAcquireWriteTimeout(l, timeForever))
        relFatalError("Failed to acquire write lock (too many waiting writers?)");
}
 
#ifdef CX_LOCK_DEBUG
_Acquires_exclusive_lock_(*l)
    static bool rwlockLogAndAcquireWrite(_Inout_ RWLock* l, const char* name,
                                        const char* filename, int line)
{
    _logFmtRwlockArgComp(CX_LOCK_DEBUG,
                         _S"Locking rwlock ${string} for WRITE at ${string}:${int}",
                         stvar(string, (string)name),
                         stvar(string, (string)filename),
                         stvar(int32, line));
    rwlockAcquireWrite(l);
    return true;
}
 
#define rwlockAcquireWrite(l) rwlockLogAndAcquireWrite(l, #l, __FILE__, __LINE__)
#endif
 
_Releases_shared_lock_(*l) _meta_inline bool rwlockReleaseRead(_Inout_ RWLock* l)
{
    devAssert(RWLOCK_READERS(atomicLoad(uint32, &l->state, Relaxed)) > 0);
    uint32 oldstate = atomicFetchSub(uint32, &l->state, RWLOCK_READ_ADD, Release);
 
    // If we were the last reader and any writers are waiting, unblock one
    if (RWLOCK_READERS(oldstate) == 1 && RWLOCK_WRITERS(oldstate) > 0) {
        devVerify(atomicFetchAdd(int32, &l->wftx.val, 1, Relaxed) == 0);
        futexWake(&l->wftx);
    }
 
    return true;
}
 
#ifdef CX_LOCK_DEBUG
_Releases_shared_lock_(*l)
    static bool rwlockLogAndReleaseRead(_Inout_ RWLock* l, const char* name,
                                        const char* filename, int line)
{
    _logFmtRwlockArgComp(CX_LOCK_DEBUG,
                         _S"Releasing rwlock ${string} for READ at ${string}:${int}",
                         stvar(string, (string)name),
                         stvar(string, (string)filename),
                         stvar(int32, line));
    return rwlockReleaseRead(l);
}
 
#define rwlockReleaseRead(l) rwlockLogAndReleaseRead(l, #l, __FILE__, __LINE__)
#endif
 
_Releases_exclusive_lock_(*l) bool rwlockReleaseWrite(_Inout_ RWLock* l);
 
#ifdef CX_LOCK_DEBUG
_Releases_exclusive_lock_(*l)
    static bool rwlockLogAndReleaseWrite(_Inout_ RWLock* l, const char* name,
                                        const char* filename, int line)
{
    _logFmtRwlockArgComp(CX_LOCK_DEBUG,
                         _S"Releasing rwlock ${string} for WRITE at ${string}:${int}",
                         stvar(string, (string)name),
                         stvar(string, (string)filename),
                         stvar(int32, line));
    return rwlockReleaseWrite(l);
}
 
#define rwlockReleaseWrite(l) rwlockLogAndReleaseWrite(l, #l, __FILE__, __LINE__)
#endif
 
_Releases_exclusive_lock_(*l)
    _Acquires_shared_lock_(*l) bool rwlockDowngradeWrite(_Inout_ RWLock* l);
 
void rwlockDestroy(_Pre_valid_ _Post_invalid_ RWLock* l);
 
CX_C_END
 
// end of thread_rwlock group