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Simplify lock as mutex should be released by the thread that performe…
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…d the initial lock to be portable
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@P-p-H-d
P-p-H-d committed Nov 26, 2024
1 parent f6d1b16 commit 50d4e15
Showing 1 changed file with 20 additions and 44 deletions.
64 changes: 20 additions & 44 deletions m-shared-ptr.h
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Original file line number Diff line number Diff line change
Expand Up @@ -381,8 +381,6 @@ static inline void M_F(name, _write_read2_unlock)(shared_t *out, const shared_t
type data; /* Allow safe casting from shared_t* to type* */ \
atomic_uint cpt; /* Owner counter that acquire the data */ \
m_mutex_t lock; /* Lock to modify the data */ \
atomic_uint num_reader; /* Number of reader threads that read the data */ \
atomic_uint num_waiting_writer; /* Number of waiting writing threads that wants to modify data */ \
m_cond_t there_is_data; /* cond var sent if there a new data added */ \
M_IF_METHOD(FULL_P, oplist)( /* cond var has meaning if it can be full */ \
m_cond_t there_is_slot; /* cond var sent if there is a free slot */ \
Expand All @@ -407,8 +405,6 @@ static inline void M_F(name, _init_lock)(shared_t *out) \
{ \
atomic_init(&out->cpt, 1); \
m_mutex_init(out->lock); \
atomic_init(&out->num_reader, 0); \
atomic_init(&out->num_waiting_writer, 0); \
m_cond_init(out->there_is_data); \
M_IF_METHOD(FULL_P, oplist)(m_cond_init(out->there_is_slot), (void)0); \
} \
Expand All @@ -420,32 +416,10 @@ static inline void M_F(name, _clear_lock)(shared_t *out) \
M_IF_METHOD(FULL_P, oplist)(m_cond_clear(out->there_is_slot), (void)0); \
} \
\
fattr void M_F(name, _read_lock)(const shared_t *out); \
fattr void M_F(name, _read_lock)(const shared_t *out) \
static inline void M_F(name, _read_lock)(const shared_t *out) \
{ \
shared_t *self = (shared_t *)(uintptr_t)out; \
m_core_backoff_ct backoff; \
m_core_backoff_init(backoff); \
while (true) { \
unsigned int num = atomic_load(&self->num_reader); \
/* To avoid reader threads that starve writer threads \
Disable sharing of lock for reader threads if some writer thread \
waits */ \
/* Otherwise try to reuse the lock opened by another reader thread */ \
if (num != 0 \
&& atomic_load(&self->num_waiting_writer) == 0 \
&& atomic_compare_exchange_strong(&self->num_reader, &num, num+1)) { \
break; \
} \
/* Otherwise try to get the lock ourself */ \
if (M_LIKELY(m_mutex_trylock(self->lock))) { \
atomic_store(&self->num_reader, 1); \
break; \
} \
/* Perform exponential backoff to avoid monopolizing the memory bus */ \
m_core_backoff_wait(backoff); \
} \
m_core_backoff_clear(backoff); \
m_mutex_lock (self->lock); \
} \
\
static inline void M_F(name, _read_wait)(const shared_t *out) \
Expand All @@ -457,46 +431,35 @@ static inline void M_F(name, _read_wait)(const shared_t *out) \
static inline void M_F(name, _read_unlock)(const shared_t *out) \
{ \
shared_t *self = (shared_t *)(uintptr_t)out; \
unsigned int num = atomic_fetch_sub(&self->num_reader, 1); \
if (num == 1) { \
/* We are the last reader thread: release the lock */ \
m_mutex_unlock(self->lock); \
} \
m_mutex_unlock (self->lock); \
} \
\
static inline void M_F(name, _write_lock)(shared_t *out) \
{ \
atomic_fetch_add(&out->num_waiting_writer, 1); \
m_mutex_lock (out->lock); \
atomic_fetch_sub(&out->num_waiting_writer, 1); \
M_ASSERT(atomic_load(&out->num_reader) == 0); \
} \
\
static inline void M_F(name, _write_wait)(shared_t *out) \
{ \
M_ASSERT(atomic_load(&out->num_reader) == 0); \
M_IF_METHOD(FULL_P, oplist)( \
m_cond_wait(out->there_is_slot, out->lock); \
,) \
,(void) out;) \
} \
\
static inline void M_F(name, _write_signal)(shared_t *out) \
{ \
M_ASSERT(atomic_load(&out->num_reader) == 0); \
m_cond_broadcast(out->there_is_data); \
} \
\
static inline void M_F(name, _free_signal)(shared_t *out) \
{ \
M_ASSERT(atomic_load(&out->num_reader) == 0); \
M_IF_METHOD(FULL_P, oplist)( \
m_cond_broadcast(out->there_is_slot); \
, ) \
, (void) out;) \
} \
\
static inline void M_F(name, _write_unlock)(shared_t *out) \
{ \
M_ASSERT(atomic_load(&out->num_reader) == 0); \
m_mutex_unlock (out->lock); \
} \
\
Expand Down Expand Up @@ -546,7 +509,6 @@ fattr void M_F(name, _write_read2_lock)(shared_t *out, const shared_t *src1, con
fattr void M_F(name, _write_read2_lock)(shared_t *out, const shared_t *src1, const shared_t *src2) \
{ \
/* We can have out == src1 or out == src2 or src1 == src2 */ \
/* if src1 == src2, nothing special to do (read_lock are compatible each other )*/ \
if (out == src1) { \
if (out == src2) { \
M_F(name, _write_lock)(out); \
Expand All @@ -568,6 +530,17 @@ fattr void M_F(name, _write_read2_lock)(shared_t *out, const shared_t *src1, con
M_F(name, _write_lock)(out); \
} \
return; \
} else if (src1 == src2) { \
if (out < src1) { \
/* out < src1 = src2 */ \
M_F(name, _write_lock)(out); \
M_F(name, _read_lock)(src1); \
} else { \
/* src1 = src2 < out */ \
M_F(name, _read_lock)(src1); \
M_F(name, _write_lock)(out); \
} \
return; \
} \
/* See above */ \
if (src1 > src2) { \
Expand Down Expand Up @@ -596,7 +569,6 @@ fattr void M_F(name, _write_read2_unlock)(shared_t *out, const shared_t *src1, c
fattr void M_F(name, _write_read2_unlock)(shared_t *out, const shared_t *src1, const shared_t *src2) \
{ \
/* We can have out == src1 or out == src2 or src1 == src2 */ \
/* if src1 == src2, nothing special to do (read_lock are compatible each other )*/ \
if (out == src1) { \
if (out == src2) { \
M_F(name, _write_unlock)(out); \
Expand All @@ -610,6 +582,10 @@ fattr void M_F(name, _write_read2_unlock)(shared_t *out, const shared_t *src1, c
M_F(name, _read_unlock)(src1); \
M_F(name, _write_unlock)(out); \
return; \
} else if (src1 == src2) { \
M_F(name, _read_unlock)(src1); \
M_F(name, _write_unlock)(out); \
return ; \
} \
/* NOTE: No need to order the unlock */ \
M_F(name, _read_unlock)(src1); \
Expand Down

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