Re: Question on Threads
On 2007-11-22 23:15:42 -0800, Ravi <v.r.sankar@gmail.com> said:
Hi,
Just wanted to clarify. Please correct me if I went wrong anywhere.
Threads seize their current execution in two ways
I think you meant "cease", as in to stop or desist, not "seize", to
take by force...
1) When they encounter a synchronized block and the object lock is not
available. They would be put in a Object Lock Monitor Queue. This
queue is managed by JVM. That is object lock acquiring and releasing
is automatically taken care by JVM on behalf of the thread
(programmer).
2) When the thread calls wait() from a synchronized block. It is then
put in Object's wait queue for which it acquired the lock and the lock
is released. Notify() by another thread brings it backs to life and
the fight for Object lock begins when it becomes the current execution
thread. The wait() and notify() have to programmed explicitly.
Threads are also likely to be suspended any time they call a blocking
system service: even reading from a file, on most OSes, makes a thread
eligible for suspension so that the OS can schedule the disk read while
allowing other threads to use the CPU while the IO-bound thread waits
for its data.
There are also explicit locks that may or may not be implemented using
synchronization and wait()/notify() in the java.util.concurrent
package. On some platforms, there are native equivalents of the same
locking tools that are much faster than a pure-Java implementation
would be. Attempting to acquire a lock that isn't available will also
block the calling thread.