Historically, Mac OS X uses the Mach-O executable format, which does not support thread local storage data section found on most operating systems using ELF executable format (here is how ELF handles thread local storage as documented by Ulrich Drepper). If you try to compile a program using __thread modifier, you'd get the following error.
2014-05-23 01:41:40.056 customtype44170:1b03 +NSUndoManager(NSInternal) endTopLevelGroupings is only safe to invoke on the main thread. This is a message coming from Mac OS itself, and it's my understanding that the event loop is in fact running by then. Multitasking is of two types: Processor based and thread based. Processor based multitasking is totally managed by the OS, however multitasking through multithreading can be controlled by the programmer to some extent. The concept of multi-threading needs proper understanding of these two terms – a process and a thread. A process is a program.
However, it has been suggested that pthread_getspecific() has a fast implementation on Mac OS X. The pthreads thread specific functions are POSIX API facility for thread local storage (TLS).
On Mac OS X, pthread_getspecific() for i386 takes exactly three instructions. It is similar to ELF handling of TLS on i386, in the sense that both use the GS segment to point to a thread control block. However, the difference is that ELF only stores the thread pointer in the thread control block, which is then used to calculate the address of the thread local storage data section for that thread. On Mac OS X, pthread specific values are allocated from the thread control block in the GS segment. This saves another indirect reference, so that could be faster.
The way Mac OS X implements pthread_getspecific() for ppc target is more complicated. First, it looks up from the COMMPAGE (defined in cpu_capabilities.h) the address to several possible pthread_getspecific() functions implemented by the mach kernel, and branch there. From there, thread control block is either obtained from SPRG3 (special purpose register #3), or by an ultra-fast trap. The SPRG3 points to thread control block where pthread specifics are allocated from, so the approach is comparable to using GS segment on i386. The ultra-fast trap approach, despite its name, is a slower fall-back approach that appeals to the task scheduler to find out which thread is currently running.
There is no reason why pthread_getspecific() couldn't be implemented as efficiently as compiler's thread local storage variables. However, with __thread, the compiler could cache the address for the thread local variable instance and reuse it in the current function. If several functions are inlined, all of them could use the same pre-computed address. With pthread_getspecific(), the compiler doesn't know that the address to the pthread specific variable can be reused. It has to call the function again whenever the value is asked. For this reason, Mac OS X also provides inlined version of pthread_getspecific() to get rid of the function call overhead, as well as allowing the compiler to pre-compute the offset into the thread control block whenever possible.
I don't know how other operating systems implement pthread_getspecific(), but if they already support thread local storage variables, they should be able to implement pthread specific like this to achieve the efficiency as expected on Mac OS X:
This is inspired by pthread_tsd.c in Mac OS X Libc. Notice that, unlike their Libc, we can implement pthread_getspecific() and pthread_setspecific() using trivial inline functions or macros that access the specifics array.
Therefore, my recommendation is to use POSIX pthread specific in your program, which will work on any POSIX including Mac OS X. If your operating system has a slow POSIX pthread specific implementation, but the compiler has thread local storage support, then you can roll your fast pthread specific like shown above.
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What is Thread?
https://vendorsoftware.mystrikingly.com/blog/cryptus-mac-os. A thread is a flow of execution through the process code, with its own program counter that keeps track of which instruction to execute next, system registers which hold its current working variables, and a stack which contains the execution history.
A thread shares with its peer threads few information like code segment, data segment and open files. When one thread alters a code segment memory item, all other threads see that.
A thread is also called a lightweight process. Threads provide a way to improve application performance through parallelism. Making a craps table. Threads represent a software approach to improving performance of operating system by reducing the overhead thread is equivalent to a classical process.
Each thread belongs to exactly one process and no thread can exist outside a process. Each thread represents a separate flow of control. Threads have been successfully used in implementing network servers and web server. They also provide a suitable foundation for parallel execution of applications on shared memory multiprocessors. Alphabeta asteroids (itch) mac os. The following figure shows the working of a single-threaded and a multithreaded process.
Difference between Process and Thread
| S.N. | Process | Thread |
|---|---|---|
| 1 | Process is heavy weight or resource intensive. | Thread is light weight, taking lesser resources than a process. |
| 2 | Process switching needs interaction with operating system. | Thread switching does not need to interact with operating system. |
| 3 | In multiple processing environments, each process executes the same code but has its own memory and file resources. | All threads can share same set of open files, child processes. |
| 4 | If one process is blocked, then no other process can execute until the first process is unblocked. | While one thread is blocked and waiting, a second thread in the same task can run. |
| 5 | Multiple processes without using threads use more resources. | Multiple threaded processes use fewer resources. |
| 6 | In multiple processes each process operates independently of the others. | One thread can read, write or change another thread's data. |
Advantages of Thread
- Threads minimize the context switching time.
- Use of threads provides concurrency within a process.
- Efficient communication.
- It is more economical to create and context switch threads.
- Threads allow utilization of multiprocessor architectures to a greater scale and efficiency.
Types of Thread
Threads are implemented in following two ways −
User Level Threads − User managed threads.
Kernel Level Threads − Operating System managed threads acting on kernel, an operating system core.
User Level Threads
In this case, the thread management kernel is not aware of the existence of threads. The thread library contains code for creating and destroying threads, for passing message and data between threads, for scheduling thread execution and for saving and restoring thread contexts. The application starts with a single thread.
Advantages
- Thread switching does not require Kernel mode privileges.
- User level thread can run on any operating system.
- Scheduling can be application specific in the user level thread.
- User level threads are fast to create and manage.
Disadvantages
- In a typical operating system, most system calls are blocking.
- Multithreaded application cannot take advantage of multiprocessing.
Kernel Level Threads
In this case, thread management is done by the Kernel. There is no thread management code in the application area. Kernel threads are supported directly by the operating system. Any application can be programmed to be multithreaded. All of the threads within an application are supported within a single process.
Tipelau mac os. The Kernel maintains context information for the process as a whole and for individuals threads within the process. Scheduling by the Kernel is done on a thread basis. The Kernel performs thread creation, scheduling and management in Kernel space. Kernel threads are generally slower to create and manage than the user threads.
Advantages
Threaded Mac Os Sierra
- Kernel can simultaneously schedule multiple threads from the same process on multiple processes.
- If one thread in a process is blocked, the Kernel can schedule another thread of the same process.
- Kernel routines themselves can be multithreaded.
Disadvantages
- Kernel threads are generally slower to create and manage than the user threads.
- Transfer of control from one thread to another within the same process requires a mode switch to the Kernel.
Therefore, my recommendation is to use POSIX pthread specific in your program, which will work on any POSIX including Mac OS X. If your operating system has a slow POSIX pthread specific implementation, but the compiler has thread local storage support, then you can roll your fast pthread specific like shown above.
- Operating System Tutorial
- OS - Exams Questions with Answers
- Operating System Useful Resources
- Selected Reading
What is Thread?
https://vendorsoftware.mystrikingly.com/blog/cryptus-mac-os. A thread is a flow of execution through the process code, with its own program counter that keeps track of which instruction to execute next, system registers which hold its current working variables, and a stack which contains the execution history.
A thread shares with its peer threads few information like code segment, data segment and open files. When one thread alters a code segment memory item, all other threads see that.
A thread is also called a lightweight process. Threads provide a way to improve application performance through parallelism. Making a craps table. Threads represent a software approach to improving performance of operating system by reducing the overhead thread is equivalent to a classical process.
Each thread belongs to exactly one process and no thread can exist outside a process. Each thread represents a separate flow of control. Threads have been successfully used in implementing network servers and web server. They also provide a suitable foundation for parallel execution of applications on shared memory multiprocessors. Alphabeta asteroids (itch) mac os. The following figure shows the working of a single-threaded and a multithreaded process.
Difference between Process and Thread
| S.N. | Process | Thread |
|---|---|---|
| 1 | Process is heavy weight or resource intensive. | Thread is light weight, taking lesser resources than a process. |
| 2 | Process switching needs interaction with operating system. | Thread switching does not need to interact with operating system. |
| 3 | In multiple processing environments, each process executes the same code but has its own memory and file resources. | All threads can share same set of open files, child processes. |
| 4 | If one process is blocked, then no other process can execute until the first process is unblocked. | While one thread is blocked and waiting, a second thread in the same task can run. |
| 5 | Multiple processes without using threads use more resources. | Multiple threaded processes use fewer resources. |
| 6 | In multiple processes each process operates independently of the others. | One thread can read, write or change another thread's data. |
Advantages of Thread
- Threads minimize the context switching time.
- Use of threads provides concurrency within a process.
- Efficient communication.
- It is more economical to create and context switch threads.
- Threads allow utilization of multiprocessor architectures to a greater scale and efficiency.
Types of Thread
Threads are implemented in following two ways −
User Level Threads − User managed threads.
Kernel Level Threads − Operating System managed threads acting on kernel, an operating system core.
User Level Threads
In this case, the thread management kernel is not aware of the existence of threads. The thread library contains code for creating and destroying threads, for passing message and data between threads, for scheduling thread execution and for saving and restoring thread contexts. The application starts with a single thread.
Advantages
- Thread switching does not require Kernel mode privileges.
- User level thread can run on any operating system.
- Scheduling can be application specific in the user level thread.
- User level threads are fast to create and manage.
Disadvantages
- In a typical operating system, most system calls are blocking.
- Multithreaded application cannot take advantage of multiprocessing.
Kernel Level Threads
In this case, thread management is done by the Kernel. There is no thread management code in the application area. Kernel threads are supported directly by the operating system. Any application can be programmed to be multithreaded. All of the threads within an application are supported within a single process.
Tipelau mac os. The Kernel maintains context information for the process as a whole and for individuals threads within the process. Scheduling by the Kernel is done on a thread basis. The Kernel performs thread creation, scheduling and management in Kernel space. Kernel threads are generally slower to create and manage than the user threads.
Advantages
Threaded Mac Os Sierra
- Kernel can simultaneously schedule multiple threads from the same process on multiple processes.
- If one thread in a process is blocked, the Kernel can schedule another thread of the same process.
- Kernel routines themselves can be multithreaded.
Disadvantages
- Kernel threads are generally slower to create and manage than the user threads.
- Transfer of control from one thread to another within the same process requires a mode switch to the Kernel.
Multithreading Models
Some operating system provide a combined user level thread and Kernel level thread facility. Solaris is a good example of this combined approach. In a combined system, multiple threads within the same application can run in parallel on multiple processors and a blocking system call need not block the entire process. Multithreading models are three types
Threaded Mac Os Download
- Many to many relationship.
- Many to one relationship.
- One to one relationship.
Many to Many Model
The many-to-many model multiplexes any number of user threads onto an equal or smaller number of kernel threads.
The following diagram shows the many-to-many threading model where 6 user level threads are multiplexing with 6 kernel level threads. In this model, developers can create as many user threads as necessary and the corresponding Kernel threads can run in parallel on a multiprocessor machine. This model provides the best accuracy on concurrency and when a thread performs a blocking system call, the kernel can schedule another thread for execution.
Threaded Mac Os X
Many to One Model
Many-to-one model maps many user level threads to one Kernel-level thread. Thread management is done in user space by the thread library. When thread makes a blocking system call, the entire process will be blocked. Only one thread can access the Kernel at a time, so multiple threads are unable to run in parallel on multiprocessors.
If the user-level thread libraries are implemented in the operating system in such a way that the system does not support them, then the Kernel threads use the many-to-one relationship modes.
Threaded Mac Os Catalina
One to One Model
There is one-to-one relationship of user-level thread to the kernel-level thread. This model provides more concurrency than the many-to-one model. As aventuras de ovoide mac os. It also allows another thread to run when a thread makes a blocking system call. It supports multiple threads to execute in parallel on microprocessors.
Disadvantage of this model is that creating user thread requires the corresponding Kernel thread. OS/2, windows NT and windows 2000 use one to one relationship model.
Difference between User-Level & Kernel-Level Thread
| S.N. | User-Level Threads | Kernel-Level Thread |
|---|---|---|
| 1 | User-level threads are faster to create and manage. | Kernel-level threads are slower to create and manage. |
| 2 | Implementation is by a thread library at the user level. | Operating system supports creation of Kernel threads. |
| 3 | User-level thread is generic and can run on any operating system. | Kernel-level thread is specific to the operating system. |
| 4 | Multi-threaded applications cannot take advantage of multiprocessing. | Kernel routines themselves can be multithreaded. |
