erlang进程的优先级

/* process priorities */
#define PRIORITY_MAX          0
#define PRIORITY_HIGH         1
#define PRIORITY_NORMAL       2
#define PRIORITY_LOW          3
#define NPRIORITY_LEVELS      4

process_flag(priority, Level)
    This sets the process priority. Level is an atom. There are currently four priority levels: low, normal, high, and max. The default priority level is normal. NOTE: The max priority level is reserved for internal use in the Erlang runtime system, and should not be used by others.
    Internally in each priority level processes are scheduled in a round robin fashion.
    Execution of processes on priority normal and priority low will be interleaved. Processes on priority low will be selected for execution less frequently than processes on priority normal.
    When there are runnable processes on priority high no processes on priority low, or normal will be selected for execution. Note, however, that this does not mean that no processes on priority low, or normal will be able to run when there are processes on priority high running. On the runtime system with SMP support there might be more processes running in parallel than processes on priority high, i.e., a low, and a high priority process might execute at the same time.
    When there are runnable processes on priority max no processes on priority low, normal, or high will be selected for execution. As with the high priority, processes on lower priorities might execute in parallel with processes on priority max.
    Scheduling is preemptive. Regardless of priority, a process is preempted when it has consumed more than a certain amount of reductions since the last time it was selected for execution.
    NOTE: You should not depend on the scheduling to remain exactly as it is today. Scheduling, at least on the runtime system with SMP support, is very likely to be modified in the future in order to better utilize available processor cores.
    There is currently no automatic mechanism for avoiding priority inversion, such as priority inheritance, or priority ceilings. When using priorities you have to take this into account and handle such scenarios by yourself.
    Making calls from a high priority process into code that you don't have control over may cause the high priority process to wait for a processes with lower priority, i.e., effectively decreasing the priority of the high priority process during the call. Even if this isn't the case with one version of the code that you don't have under your control, it might be the case in a future version of it. This might, for example, happen if a high priority process triggers code loading, since the code server runs on priority normal.
    Other priorities than normal are normally not needed. When other priorities are used, they need to be used with care, especially the high priority must be used with care. A process on high priority should only perform work for short periods of time. Busy looping for long periods of time in a high priority process will most likely cause problems, since there are important servers in OTP running on priority normal.

process_flag(save_calls, N)
    When there are runnable processes on priority max no processes on priority low, normal, or high will be selected for execution. As with the high priority, processes on lower priorities might execute in parallel with processes on priority max.
    N must be an integer in the interval 0..10000. If N > 0, call saving is made active for the process, which means that information about the N most recent global function calls, BIF calls, sends and receives made by the process are saved in a list, which can be retrieved with process_info(Pid, last_calls). A global function call is one in which the module of the function is explicitly mentioned. Only a fixed amount of information is saved: a tuple {Module, Function, Arity} for function calls, and the mere atoms send, 'receive' and timeout for sends and receives ('receive' when a message is received and timeout when a receive times out). If N = 0, call saving is disabled for the process, which is the default. Whenever the size of the call saving list is set, its contents are reset.

不过要慎重使用优先级，除非必要。