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Make empth_rwlock_t prefer writers

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LWP and Windows implementations already did that.  Rewrite the
pthreads implementation.

The write-bias makes the stupid play_wrlock_wanted busy wait in
dispatch() unnecessary.  Remove it.
This commit is contained in:
Markus Armbruster 2009-04-26 23:48:05 +02:00
parent 079fb286c5
commit d052239a7a
3 changed files with 47 additions and 28 deletions
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12
include/empthread.h
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@ -56,10 +56,10 @@
/* Abstract data types */
/* empth_t * represents a thread. */
/* A thread. */
typedef struct lwpProc empth_t;
/* empth_rwlock_t * represents a read-write lock */
/* A read-write lock, perferring writers */
typedef struct lwp_rwlock empth_rwlock_t;
/* Flags for empth_select(): whether to sleep on input or output */
@ -189,7 +189,7 @@ int empth_wait_for_signal(void);
/*
* Create a read-write lock.
* NAME is its name, it is used for debugging.
* Return the reade-write lock, or NULL on error.
* Return the read-write lock, or NULL on error.
*/
empth_rwlock_t *empth_rwlock_create(char *name);
@ -209,9 +209,9 @@ void empth_rwlock_wrlock(empth_rwlock_t *rwlock);
/*
* Lock RWLOCK for reading.
* A read-write lock can be locked for reading only when it is not
* locked for writing. If this is not the case, put the current
* thread to sleep until it is. Must not starve writers, and may
* sleep to avoid that.
* locked for writing, and no other thread is attempting to lock it
* for writing. If this is not the case, put the current thread to
* sleep until it is.
*/
void empth_rwlock_rdlock(empth_rwlock_t *rwlock);