tailieunhanh - Operating Systems Design and Implementation, Third Edition phần 3

Hơn nữa, nếu hệ thống là một đa, với hai hoặc nhiều CPU, vô hiệu hóa ngắt chỉ ảnh hưởng đến CPU thực hiện các hướng dẫn vô hiệu hóa. Những người khác sẽ tiếp tục chạy và có thể truy cập bộ nhớ chia sẻ. Mặt khác, đó là thường xuyên thuận tiện cho các hạt nhân chính nó để vô hiệu hóa ngắt cho | Simpo PDF Merge and Split Unregistered Version - http 45 declaration at line 6822 ensures that this storage space is allocated at the very beginning of the kernel s data segment and that it is the start of a read-only section of memory. The compiler puts a magic number here so boot can verify that the file it loads is a valid kernel image. When compiling the complete system various string constants will be stored following this. The other data storage area defined at the .sect .bss line 6825 declaration reserves space in the kernel s normal uninitialized variable area for the kernel stack and above that some space is reserved for variables used by the exception handlers. Servers and ordinary processes have stack space reserved when an executable file is linked and depend upon the kernel to properly set the stack segment descriptor and the stack pointer when they are executed. The kernel has to do this for itself. . Interprocess Communication in MINIX 3 Processes in MINIX 3 communicate by messages using the rendezvous principle. When a process does a send the lowest layer of the kernel checks to see if the destination is waiting for a message from the sender or from ANY sender . If so the message is copied from the sender s buffer to the receiver s buffer and both processes are marked as runnable. If the destination is not waiting for a message from the sender the sender is marked as blocked and put onto a queue of processes waiting to send to the receiver. When a process does a receive the kernel checks to see if any process is queued trying to send to it. If so the message is copied from the blocked sender to the receiver and both are marked as runnable. If no process is queued trying to send to it the receiver blocks until a message arrives. In MINIX 3 with components of the operating system running as totally separate processes sometimes the rendezvous method is not quite good enough. The notify primitive is provided for precisely these .