For decades, Dennard Scaling was the gift that kept on giving. If the computer is running quickly enough, its inability to handle more than one thread at a time becomes much less of a problem. While there are a distinct set of problems that cannot be calculated in less time than the expected lifetime of the universe on a classical computer, there are many, many, many problems that can be calculated just fine that way. As computers got faster, developers created more sophisticated software.
The simplest form of multithreading is coarse-grained multithreading, in which the operating system switches to a different thread rather than sitting around waiting for the results of a calculation. The advent of caches meant that CPUs could keep small collections of instructions nearby for immediate number crunching, while multithreading ensured the CPU always had something to do.
Symmetric Multiprocessing and Symmetric Multithreading are two different things. To put it simply:. Both companies have historically deployed it strategically, offering it on some products but not on others. Pushing the Limits of Windows: Physical Memory. Pushing the Limits of Windows: Virtual Memory.
Pushing the Limits of Windows: Processes and Threads. Pushing the Limits of Windows: Handles. A Windows process is essentially container that hosts the execution of an executable image file.
Processes operate with a security context, called a token, that identifies the user account, account groups, and privileges assigned to the process. Besides basic information about a thread, including its CPU register state, scheduling priority, and resource usage accounting, every thread has a portion of the process address space assigned to it, called a stack, which the thread can use as scratch storage as it executes program code to pass function parameters, maintain local variables, and save function return addresses.
Because stacks grow downward in memory, the system places guard pages beyond the committed part of the stack that trigger an automatic commitment of additional memory called a stack expansion when accessed.
The linker defaults to a reserve of 1MB and commit of one page 4K , but developers can override these values either by changing the PE values when they link their program or for an individual thread in a call to CreateThread.
You can use a tool like Dumpbin that comes with Visual Studio to look at the settings for an executable. Condition Variables.
Condition variables communicate readiness between threads by enabling a thread to be woken up when a condition becomes true. Without condition variables, the waiting thread would have to use some form of polling to check whether the condition had become true. Condition variables work in conjunction with a mutex.
The mutex is there to ensure that only one thread at a time can access the variable. For example, the producer-consumer model can be implemented using condition variables. Suppose an application has one producer thread and one consumer thread. The producer adds data onto a queue, and the consumer removes data from the queue. If there is no data on the queue, then the consumer needs to sleep until it is signaled that an item of data has been placed on the queue.
Acquire Mutex ;. Add Item to Queue ;. If Only One Item on Queue. Signal Conditions Met ;. Release Mutex ;. The producer thread needs to signal a waiting consumer thread only if the queue was empty and it has just added a new item into that queue. If there were multiple items already on the queue, then the consumer thread must be busy processing those items and cannot be sleeping.
If there were no items in the queue, then it is possible that the con-sumer thread is sleeping and needs to be woken up. If No Items on Queue. Wait on Condition Variable ;. If Item on Queue. Until Item! The consumer thread will wait on the condition variable if the queue is empty. When the producer thread signals it to wake up, it will first check to see whether there is any-thing on the queue.
It is quite possible for the consumer thread to be woken only to find the queue empty; it is important to realize that the thread waking up does not imply that the condition is now true, which is why the code is in a repeat loop in the example.
If there is an item on the queue, then the consumer thread can handle that item; otherwise, it returns to sleep. The interaction with the mutex is interesting. The producer thread needs to acquire the mutex before adding an item to the queue. It needs to release the mutex after adding the item to the queue, but it still holds the mutex when signaling. The consumer thread cannot be woken until the mutex is released. The producer thread releases the mutex after the signaling has completed; releasing the mutex is necessary for the consumer thread to make progress.
The consumer thread acquires the mutex; it will need it to be able to safely modify the queue. If there are no items on the queue, then the consumer thread will wait for an item to be added. The call to wait on the condition variable will cause the mutex to be released, and the consumer thread will wait to be signaled.
When the consumer thread wakes up, it will hold the mutex; either it will release the mutex when it has removed an item from the queue or, if there is still nothing in the queue, it will release the mutex with another call to wait on the condition variable.
The producer thread can use two types of wake-up calls: Either it can wake up a sin-gle thread or it can broadcast to all waiting threads. Which one to use depends on the context. If there are multiple items of data ready for processing, it makes sense to wake up multiple threads with a broadcast. On the other hand, if the producer thread has added only a single item to the queue, it is more appropriate to wake up only a single thread. If all the threads are woken, it can take some time for all the threads to wake up, execute, and return to waiting, placing an unnecessary burden on the system.
Asked 8 years, 3 months ago. Active 5 years, 4 months ago. Viewed 5k times. What is the best way for worker threads to communicate with the main UI thread? Why can I not increase the quota of post messages in a queue?
Improve this question. Andrea Woody20 Woody20 9 9 silver badges 24 24 bronze badges. Post message is one way to go. But have you considered greatly lowering the number of messages? Why not only update every or messages?
The approach you are taking is correct, but there is really no point in sending enough messages to exceed the queue limit. The only things that could cause a posted message to not be received are overflowing the queue limit or having the main thread blocked, like in a Sleep or WaitFor..
What is the main thread doing while these messages are being posted? Are you also allocating another traceLineBuffer to go with each message? Maybe this is the problem. Yes, a new message and buffer are allocated for each message, as you can see from my deleting them in OnTraceLineMsg. Add a comment. Active Oldest Votes.
Improve this answer. Martin James Martin James GetQueuedCompletionStatus messagePort,
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