|
|
|
Since the wait and signal operations on semaphores and on condition variables are similar, to help you distinguish their differences and use them correctly, the following is a brief comparison.
| Semaphores | Condition Variables |
| Can be used anywhere in a program, but should not be used in a monitor | Can only be used in monitors |
| Wait() does not always block the caller (i.e., when the semaphore counter is greater than zero). | Wait() always blocks the caller. |
| Signal() either releases a blocked thread, if there is one, or increases the semaphore counter. | Signal() either releases a blocked thread, if there is one, or the signal is lost as if it never happens. |
| If Signal() releases a blocked thread, the caller and the released thread both continue. | If Signal() releases a blocked thread, the caller yields the monitor (Hoare type) or continues (Mesa Type). Only one of the caller or the released thread can continue, but not both. |
|
|
|
|