On Sat, Nov 23, 2002 at 03:58:44AM -0800, earl wrote: > What does it mean when one says that a > "kernel is interruptible but not reentrant"? A process running in the kernel can be pre-empted by an interrupt handler whenever an interrupt occurs and interrupts are not currently blocked. (cli()/sti() and friends.) (This happens whether or not the pre-empt kernel patch has been applied.) However, I'm not sure about the part of the statement that says, "not reentrant". Re-entrancy is normally when a specific function is called and, while running, gets blocked or pushed to the side in some fashion for another task to run -- which needs to run the same function. (A classic example of a function that is not re-entrant is strtok(3) from the standard C library; it uses a static variable internally, limiting an address space to running only one strtok(3) function at a time. A multithreaded application would need to use strtok_r(3) instead, which does not use static storage.) So, kernel functions that use static or otherwise global storage are not re-entrant unless they have been programmed with care to be re-entrant. Considering that most linux kernels are designed to run on SMP systems, I'm not sure if the sentence as a whole is true. But that is for smarter people to answer. :) -- It seems the power has been robbed from the founding fathers and is now firmly in the hand of the funding fathers -- Rik van Riel
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