Modifying a threads data from outside the thread

How does one modify a threads data from outside a thread?

If a thread is running a function that loops for the runtime of the appl开发者_高级运维ication, how can its data be set, changed?

How does one call functions which modify a specific threads functions?

Where do these functions belong?

The advantage and disadvantage of threads is that they share the memory space with every other thread in the process. You can use any form of data transfer you would use in single threaded applications to pass data betweens segments of you application. However, in a multi-threaded application you must use some type of synchronization to assure data integrity and prevent deadlocks.

If the "thread's data" you want to modify from outside is in the form of local variables in a function running in the thread, or thread-specific data created with the __thread extension, then the only way you can modify them from outside (modulo code with UB that's technically just trashing memory) is by having the thread take the addresses of its variables and store that somewhere where other threads can see it (either in a global variable, or at a location passed in via the thread start function's void * argument.

Also note that, as rerun pointed out, you have to use some method of synchronization if multiple threads are accessing the same data. The only standard/portable synchronization methods are the pthread ones: pthread_mutex_lock etc., but you can also use assembly or compiler intrinsics (like __sync_* in gcc).