Local synchronisation

ugenn · 08-01-2004, 03:17 PM

Does any local synchronisation mechanism (eg mutexes, but local to a process) exist in Linux and what are the system calls involved?

itsme86 · 08-01-2004, 03:42 PM

I know pthreads has mutex support built right into the library, but I very rarely build threaded apps so I couldn't tell you what the function calls are off the top of my head.

ugenn · 08-01-2004, 03:50 PM

Thanks, I'll look into it.

infamous41md · 08-01-2004, 03:59 PM

pthread mutexes, condition variables, and read/write locks are implemented as user space libraries, there are no system calls directly associated with functions that operate on them - there are a number of different ways to implement them. ie FIFOS, mmap'd files and so on. on the other hand, you have SYSV semaphores, which are implemented in the kernel as system calls. see man ipc, which will lead u to semop and friends. for pthread functions, try:
man pthread_mutex_lock, man pthread_cond_wait, man pthread_rwlock_rdlock

Mara · 08-01-2004, 05:23 PM

You got a list of man command you may try to look into, I'd add that to use pthread* functions you'd need to link your program with -lpthread option.

JanusPaul · 09-14-2005, 01:01 AM

Question:

If I have a function setup for common reference of searching/push/poping a pointer chain structure system, with, lets say syntax for read locking when merely searching the chain, and write locking for when chain elements are created/deleted, is there anyway to allow the same thread to call the function from within the function using BOTH a write and read lock?

Code:

	#define	PTHREAD_LOCK_TYPE					pthread_rwlock_t
	#define	PTHREAD_LOCK_RDLOCK					pthread_rwlock_rdlock
	#define	PTHREAD_LOCK_WRLOCK					pthread_rwlock_wrlock
	#define	PTHREAD_LOCK_UNLOCK					pthread_rwlock_unlock
	#define	PTHREAD_LOCK_INITIALIZER				PTHREAD_RWLOCK_INITIALIZER

		extern	"C" ServerUserPtr				userInfo( Flags flags, ... )
	{
		if ( flags & FLAG_MODE_SELECT )
			PTHREAD_LOCK_RDLOCK( &gUserLock );
		else
			PTHREAD_LOCK_WRLOCK( &gUserLock );

		switch ( flags & 0x000000FF )
		{
			case FLAG_MODE_SELECT:
				(search)
				break;
			case FLAG_MODE_DELETE:
				(delete)
				break;
			case FLAG_MODE_CREATE:
				if ( userInfo( FLAG_MODE_SELECT | FLAG_DATA_USER_USERID, userID ) )
					break;
				(create)
				break;
		}

		PTHREAD_LOCK_UNLOCK( &gUserLock );

		return userPtr;
	}

A condensed version of http://dls.palacecommunity.com/open/...sion_users.cpp

Basically, during the creation phase, userInfo will call itself inorder to make user 'userID' is unique for this user. Is there anyway to allow recursive read/write calls to the same function with both a read/write lock under the same thread to make something like this possible? Mutex locks recursive calling within the same thread works, but, it would be nice to have read/write locking instead - quicker access to shared resources.

JanusPaul · 09-14-2005, 01:16 PM

Nobody can help with this mutex rwlock stuff?

JanusPaul · 09-14-2005, 05:38 PM

Nevermind, my screw up.