erlang otp包里的 cryto很好的贯彻了下面的原则,是个很好的教材:
9 Drivers
This chapter provides a (very) brief overview on how to write efficient drivers. It is assumed that you already have a good understanding of drivers.
9.1 Drivers and concurrency
The run-time system will always take a lock before running any code in a driver.
By default, that lock will be at the driver level, meaning that if several ports has been opened to the same driver, only code for one port at the same time can be running.
A driver can be configured to instead have one lock for each port.
If a driver is used in a functional way (i.e. it holds no state, but only does some heavy calculation and returns a result), several ports with registered names can be opened beforehand and the port to be used can be chosen based on the scheduler ID like this:
-define(PORT_NAMES(),
{some_driver_01, some_driver_02, some_driver_03, some_driver_04,
some_driver_05, some_driver_06, some_driver_07, some_driver_08,
some_driver_09, some_driver_10, some_driver_11, some_driver_12,
some_driver_13, some_driver_14, some_driver_15, some_driver_16}).
client_port() ->
element(erlang:system_info(scheduler_id) rem tuple_size(?PORT_NAMES()) + 1,
?PORT_NAMES()).
As long as there are no more than 16 schedulers, there will never be any lock contention on the port lock for the driver.
9.2 Avoiding copying of binaries when calling a driver
There are basically two ways to avoid copying a binary that is sent to a driver.
If the Data argument for port_control/3 is a binary, the driver will be passed a pointer to the contents of the binary and the binary will not be copied. If the Data argument is an iolist (list of binaries and lists), all binaries in the iolist will be copied.
Therefore, if you want to send both a pre-existing binary and some additional data to a driver without copying the binary, you must call port_control/3 twice; once with the binary and once with the additional data. However, that will only work if there is only one process communicating with the port (because otherwise another process could call the driver in-between the calls).
Another way to avoid copying binaries is to implement an outputv callback (instead of an output callback) in the driver. If a driver has an outputv callback, refc binaries passed in an iolist in the Data argument for port_command/2 will be passed as references to the driver.
9.3 Returning small binaries from a driver
The run-time system can represent binaries up to 64 bytes as heap binaries. They will always be copied when sent in a messages, but they will require less memory if they are not sent to another process and garbage collection is cheaper.
If you know that the binaries you return are always small, you should use driver API calls that do not require a pre-allocated binary, for instance driver_output() or driver_output_term() using the ERL_DRV_BUF2BINARY format, to allow the run-time to construct a heap binary.
9.4 Returning big binaries without copying from a driver
To avoid copying data when a big binary is sent or returned from the driver to an Erlang process, the driver must first allocate the binary and then send it to an Erlang process in some way.
Use driver_alloc_binary() to allocate a binary.
There are several ways to send a binary created with driver_alloc_binary().
•From the control callback, a binary can be returned provided that set_port_control() has been called with the flag value PORT_CONTROL_FLAG_BINARY.
•A single binary can be sent with driver_output_binary().
•Using driver_output_term() or driver_send_term(), a binary can be included in an Erlang term.
分享到:
相关推荐
erlang-24.3.3-1.el9.x86_64.rpm centos
NULL 博文链接:https://jianshi-dlw.iteye.com/blog/1179745
binpp::1234:Erlang二进制漂亮打印机
niffed 是一个包装器,可让您在 Erlang 驱动程序中使用 nif API。 甚至可以同时加载与驱动程序和 nif 相同的代码。 nif 调用是通过驱动程序控制接口通过简单的调度程序进行的。 这使得将 nif 代码移植到驱动程序中...
erlang-19.3.2
NULL 博文链接:https://jianshi-dlw.iteye.com/blog/1179731
Erlang and OTP in Action Martin Logan, Eric Merritt, and Richard Carlsson MEAP Began: August 2008 Softbound print: May 2010 (est.) | 500 pages ISBN: 1933988789 Part One: Getting Past Pure Erlang; ...
mongodb-erlang:Erlang的MongoDB驱动程序
https://github.com/rabbitmq/erlang-rpm.git源码在centos6.8x64系统下编译的rpm文件
GraphQL-Erlang教程该存储库包含有关graphql-erlang系统的教程。 它实现了SWAPI(的子集)作为示例项目,以阐明应如何在完整实现中使用该系统。 这个想法是,它可以用作您自己的GraphQL模式实现的起点。文献资料该...
erlang-23.1-1.el8.x86_ ,erlang官网下载很慢,所以提供该下载链接。
awesome-erlang:精选的Erlang库,资源和闪亮内容的精选列表
金属箔:高性能Erlang缓存编译器
erlang-crypto-19.3.6.4-1.el7.x86_64.rpm
适用于Oracle数据库的Erlang驱动程序和Ecto适配器 特征 使用准备好的语句功能。 使用绑定变量。 调用存储过程。 调用存储的函数。 使用游标变量。 使用返回子句。 更新批处理。 行预取。 入门 % % Set ...
esl-erlang_19.0~centos~6_amd64.rpm
球拍位语法:球拍的Erlang样式二进制位串
某流水过千W的erlang游戏后端, 具体自行查看吧,可以学习的地方很多,适合erlang进阶的人
esl-erlang_23.0和rabbitmq-3.8.4windows版本 直接下载安装就行,可以直接下载就可安装,非常的方便 ,欢迎大家下载 注意事项: 1. Erlang版本和RabbitMQ版本要配套 (Erlang23.0, RabbitMQ3.8.4) 2. amd芯片请乖乖...
浮标:高性能Erlang HTTP 1.1客户端