Concurrency并发 vs. Parallelism执行

Many-to-One

               GNU Portable Threads

多对一即多个用户线程映射到单个内核线程  该模式用的少

一个线程阻塞会导致所有线程阻塞

多线程可能无法在多核系统上并行运行，因为同一时间内核中可能只有一个线程

• Concurrent execution on single-core system:
• 
• Parallelism on a multi-core system:
• 

  Multithreading Models

• Many-to-One
• One-to-One
• Many-to-Many
• Many user-level threads mapped to single kernel thread
• One thread blocking causes all to block
• Multiple threads may not run in parallel on multicore system because only one may be in kernel at a time
• Few systems currently use this model
• Examples:
  • Solaris Green Threads

One-to-One

Each user-level thread maps to kernel thread Creating a user-level thread creates a kernel thread More concurrency than many-to-one Number of threads per process sometimes restricted due to overhead Examples

• Windows Linux

每个用户级线程映射到内核线程

创建一个用户级线程会创建一个内核线程

比多对一更高的并发性

每个进程的线程数有时会因开销而受到限制

Many-to-Many Model

Allows many user level threads to be mapped to many kernel threads Allows the  operating system to create a sufficient number of kernel threads Windows  with the ThreadFiber package

允许将许多用户级线程映射到许多内核线程上

允许操作系统创建足够数量的内核线程

• • Otherwise not very common
  • 

Two-level Model

Similar to M:M, except that it allows a user thread to be bound to kernel thread