A nonthreaded environment has only one thread of control. Synchronous and asynchronous signals are delivered to the process.
In a multithreaded environment, multiple threads represent multiple threads of control. A synchronous signal is always delivered for the thread that caused the exception. An asynchronous signal is delivered for the first executing thread for which delivery of the signal is enabled.
You can specify that an asynchronous signal will be delivered for a thread or set of threads. Unmask the signal for a set of threads to enable signal delivery for these threads. Mask the signal for all other threads to disable signal delivery. The kernel holds a signal until it executes a thread for which delivery of the signal is enabled.
