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Rewrite Read / Write lock to be less costly

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Patrick Pelissier committed 2024-03-26 22:41:41 +01:00
1 parent cfab3cf0cf
commit 7575681e27
1 file changed
+19 -52
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m-concurrent.h
+19 -52
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@@ -777,9 +777,7 @@
typedef struct M_F(name, _s) { \
struct M_F(name, _s) *self; \
m_mutex_t lock; \
m_cond_t rw_done; \
size_t read_count; \
bool writer_waiting; \
atomic_uint num_reader; /* number of reader threads */ \
m_cond_t there_is_data; /* condition raised when there is data */ \
type data; \
} concurrent_t[1]; \
@@ -796,11 +794,9 @@
M_F(name, _internal_init)(concurrent_t out) \
{ \
m_mutex_init(out->lock); \
m_cond_init(out->rw_done); \
atomic_store(&out->num_reader, 0); \
m_cond_init(out->there_is_data); \
out->self = out; \
out->read_count = 0; \
out->writer_waiting = false; \
M_C0NCURRENT_CONTRACT(out); \
} \
\
@@ -809,7 +805,6 @@
{ \
M_C0NCURRENT_CONTRACT(out); \
m_mutex_clear(out->lock); \
m_cond_clear(out->rw_done); \
m_cond_clear(out->there_is_data); \
out->self = NULL; \
} \
@@ -819,12 +814,18 @@
{ \
M_C0NCURRENT_CONTRACT(out); \
struct M_F(name, _s) *self = out->self; \
m_mutex_lock (self->lock); \
while (self->writer_waiting == true) { \
m_cond_wait(self->rw_done, self->lock); \
while (true) { \
unsigned int num = atomic_load(&self->num_reader); \
if (num != 0 \
&& atomic_compare_exchange_strong(&self->num_reader, &num, num+1)) { \
break; \
} \
if (m_mutex_trylock(self->lock)) { \
atomic_store(&self->num_reader, 1); \
break; \
} \
/* TODO: exponential backoff */ \
} \
self->read_count ++; \
m_mutex_unlock (self->lock); \
} \
\
M_INLINE void \
@@ -832,12 +833,10 @@
{ \
M_C0NCURRENT_CONTRACT(out); \
struct M_F(name, _s) *self = out->self; \
m_mutex_lock (self->lock); \
self->read_count --; \
if (self->read_count == 0) { \
m_cond_broadcast (self->rw_done); \
unsigned int num = atomic_fetch_sub(&self->num_reader, 1); \
if (num == 1) { \
m_mutex_unlock(self->lock); \
} \
m_mutex_unlock (self->lock); \
} \
\
M_INLINE void \
@@ -845,23 +844,14 @@
{ \
M_C0NCURRENT_CONTRACT(out); \
m_mutex_lock (out->lock); \
while (out->writer_waiting == true) { \
m_cond_wait(out->rw_done, out->lock); \
} \
out->writer_waiting = true; \
while (out->read_count > 0) { \
m_cond_wait(out->rw_done, out->lock); \
} \
m_mutex_unlock (out->lock); \
M_ASSERT(atomic_load(&out->num_reader) == 0); \
} \
\
M_INLINE void \
M_F(name, _write_unlock)(concurrent_t out) \
{ \
M_C0NCURRENT_CONTRACT(out); \
m_mutex_lock (out->lock); \
out->writer_waiting = false; \
m_cond_broadcast (out->rw_done); \
M_ASSERT(atomic_load(&out->num_reader) == 0); \
m_mutex_unlock (out->lock); \
} \
\
@@ -870,45 +860,22 @@
{ \
M_C0NCURRENT_CONTRACT(out); \
struct M_F(name, _s) *self = out->self; \
M_ASSERT (self == out); \
m_mutex_lock (out->self->lock); \
self->read_count --; \
if (self->read_count == 0) { \
m_cond_broadcast (self->rw_done); \
} \
m_cond_wait(self->there_is_data, self->lock); \
while (self->writer_waiting == true) { \
m_cond_wait(self->rw_done, self->lock); \
} \
self->read_count ++; \
m_mutex_unlock (out->self->lock); \
} \
\
M_INLINE void \
M_F(name, _write_wait)(concurrent_t out) \
{ \
M_C0NCURRENT_CONTRACT(out); \
m_mutex_lock (out->lock); \
out->writer_waiting = false; \
m_cond_broadcast (out->rw_done); \
m_cond_wait(out->there_is_data, out->lock); \
while (out->writer_waiting == true) { \
m_cond_wait(out->rw_done, out->lock); \
} \
out->writer_waiting = true; \
while (out->read_count > 0) { \
m_cond_wait(out->rw_done, out->lock); \
} \
m_mutex_unlock (out->lock); \
} \
\
M_INLINE void \
M_F(name, _write_signal)(concurrent_t out) \
{ \
M_C0NCURRENT_CONTRACT(out); \
m_mutex_lock (out->lock); \
M_ASSERT(atomic_load(&out->num_reader) == 0); \
m_cond_broadcast(out->there_is_data); \
m_mutex_unlock (out->lock); \
} \