os_cpu.h

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 */

/*
 * OS-specific support functions relating to CPU and memory
 */

#ifndef INCLUDED_OS_CPU
#define INCLUDED_OS_CPU

namespace ERR
{
    const Status OS_CPU_RESTRICTED_AFFINITY = -130100;
}


//-----------------------------------------------------------------------------
// processor topology

// processor ID = [0, os_cpu_NumProcessors())
// they are a numbering of the bits of the process affinity mask where the
// least significant nonzero bit corresponds to ID 0.
// rationale: this spares users from having to deal with noncontiguous IDs,
// e.g. when administrative tools are used to restrict process affinity.


/**
 * maximum number of processors supported by the OS (determined by the
 * number of bits in an affinity mask)
 **/
static const size_t os_cpu_MaxProcessors = sizeof(uintptr_t)*CHAR_BIT;

/**
 * @return bit mask of processors that exist and are available to
 * this process.
 * its population count is by definition equal to os_cpu_NumProcessors().
 **/
uintptr_t os_cpu_ProcessorMask();

/**
 * @return the number of processors available to this process.
 *
 * note: this function is necessary because POSIX sysconf _SC_NPROCESSORS_CONF
 * is not suppored on MacOSX, else we would use that.
 **/
size_t os_cpu_NumProcessors();


//-----------------------------------------------------------------------------
// CPU and memory characteristics

/**
 * @return a rough estimate of the CPU clock frequency.
 * this is usually accurate to a few MHz and is faster than measurement loops.
 **/
double os_cpu_ClockFrequency();

/**
 * @return the size [bytes] of a MMU page (4096 on most IA-32 systems)
 **/
size_t os_cpu_PageSize();

/**
 * @return the size [bytes] of a large MMU page (4 MiB on most IA-32 systems)
 * or zero if they are not supported.
 **/
size_t os_cpu_LargePageSize();

/**
 * @return the size [MB] of physical memory as reported by the OS;
 * no caching/validation is performed.
 **/
size_t os_cpu_QueryMemorySize();

/**
 * @return the size [MB] of physical memory; caches the result of
 * os_cpu_QueryMemorySize and overrides it with a more exact value
 * if SMBIOS information is available.
 **/
size_t os_cpu_MemorySize();

/**
 * @return the current amount [MB] of available memory.
 **/
size_t os_cpu_MemoryAvailable();


//-----------------------------------------------------------------------------
// scheduling

/**
 * restrict the current thread to a set of processors.
 *
 * @param processorMask a bit mask of acceptable processors
 * (bit index i corresponds to processor i)
 * @return the previous mask
 **/
uintptr_t os_cpu_SetThreadAffinityMask(uintptr_t processorMask);

class os_cpu_ScopedSetThreadAffinityMask
{
public:
    os_cpu_ScopedSetThreadAffinityMask(uintptr_t processorMask)
        : m_previousProcessorMask(os_cpu_SetThreadAffinityMask(processorMask))
    {
    }

    ~os_cpu_ScopedSetThreadAffinityMask()
    {
        (void)os_cpu_SetThreadAffinityMask(m_previousProcessorMask);
    }

private:
    uintptr_t m_previousProcessorMask;
};


/**
 * called by os_cpu_CallByEachCPU.
 * @param processor ID of processor running the current thread for the
 * duration of this function.
 * @param cbData user-specified data passed through os_cpu_CallByEachCPU.
 **/
typedef void (*OsCpuCallback)(size_t processor, uintptr_t cbData);

/**
 * execute the specified function once on each processor.
 * this proceeds serially (the callback is never reentered) in increasing
 * order of processor ID.
 * fails if process affinity prevents running on all processors.
 **/
Status os_cpu_CallByEachCPU(OsCpuCallback cb, uintptr_t cbData);

#endif  // #ifndef INCLUDED_OS_CPU