On 05/01/2014, at 12:25 PM, James Dennett wrote: >> Also don't forget C does NOT allow malloc() to return demand >> paged memory. Malloc has to return actual memory. > > On Mac/Linux/Windows, malloc won't return committed memory. You can > malloc much more memory than your system has. (You can turn off > overcommit at the OS level on Linux, but if you want actual memory > when you call malloc then you'll need to touch each page of it.) > > I wonder why you think C doesn't allow that. All bets are off if you > exceed "resource limits" anyway.
Because the issue came up during the certification of a C compiler on HP/UX I think and the ISO committee was approached for a clarification. Which was as I reported. If malloc returns a non-NULL pointer, a subsequent memory fault is not permitted. If such a fault occurs the compiler is not conforming. In other words, if you run out of memory, malloc() has to return NULL and the program can check. So out of heap memory error is not allowed in C. Stack overflow is, of course. Naturally, the OS can delay allocation of physical memory pages until they're needed, but overcommitment is not allowed. If you think about it, this is the ONLY possible way given the set of functions available in C. There's no function to allocate address space and populate it later. If there were, the populating function could return an error code. Without such a function, any error code has to be returned by malloc. If the error is delayed any C program doing a heap allocation at ANY time could be allowed to fail at ANY time. There are no words in the C standard allowing memory to evaporate unless it is written to. -- john skaller skal...@users.sourceforge.net http://felix-lang.org ------------------------------------------------------------------------------ Rapidly troubleshoot problems before they affect your business. Most IT organizations don't have a clear picture of how application performance affects their revenue. With AppDynamics, you get 100% visibility into your Java,.NET, & PHP application. Start your 15-day FREE TRIAL of AppDynamics Pro! http://pubads.g.doubleclick.net/gampad/clk?id=84349831&iu=/4140/ostg.clktrk _______________________________________________ Felix-language mailing list Felix-language@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/felix-language
