Chapter 4 Threads. 4.1 Overview. This is what a thread has of its own: A thread id A program counter A register set A stack This is what it shares with other threads belonging to the same process: A code section A data section Other resources, such as open files.
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A traditional process with only one thread of control may be known as a heavyweight process
Java threads don’t fit the user level vs. kernel level thread API library distinction very well
For what it’s worth, note that in the Java API, the Thread class implements the Runnable interface
The overall point of the program is to find the sum of the integers less than or equal to some given upper limit
Because the run() method in the Runnable interface specification is void, it is not possible for it to return a computed value
Although, in theory, a principal advantage of threading is that the threads run concurrently, this introduces the potential for synchronization problems
From the point of view of clarity of the example, this has two disadvantages:
The name of the method that causes one thread to depend on another is join()
The authors introduce one more thread concept which isn’t directly relevant to the example
Dead: A thread enters the dead state when execution reaches the end of the run() method
Note that it may be difficult or impossible for the programmer/user to determine the relationship between a Java thread and the native environment thread or process that it is running on.
In a multi-threaded program, if one thread calls fork(), should all of the threads be duplicate, or just the calling thread?
Q: In a multi-threaded program, if one thread calls fork(), should all of the threads be duplicate, or just the calling thread?
If you’re writing code where you’re going to call exec() after fork(), use the fork() that just duplicates the one thread because they’re all going to get wiped out anyway.
In Unix, the occurrence of events is signaled like a software interrupt
1. For synchronous threads, it makes sense to deliver the signal to the thread which caused the signal to be generated. If one thread of many divided by 0, that threat should be signaled
The overall problem is one of continuously creating things, destroying them, and creating new ones again
The previous solutions don’t work in the thread pool scenario, where the user doesn’t create the thread that does the task
The lightweight process is what the threading system presents to the user level thread library