生成带有图像的pdf时，PDFkit会挂起
我想将网页呈现为PDF。 它使用单个图像，我已经读过你需要提供PDFkit的绝对URL才能使用图像，所以我的代码是：
= image_tag image_url(user.avatar) 这在以HTML格式查看时有效，并且PDFkit能够生成删除了图像的PDF。 但是，在使用图像时，它会挂起，直到我杀死服务器。 我怎样才能让它发挥作用？
这是杀死服务器时的完整输出：
2013-12-04 13:53:36.576 wkhtmltopdf[27410:507] CoreText performance note: Client called CTFontCreateWithName() using name "Arial" and got font with PostScript name "ArialMT". For best performance, only use PostScript names when calling this API. 2013-12-04 13:53:36.577 wkhtmltopdf[27410:507] CoreText performance note: Set a breakpoint on CTFontLogSuboptimalRequest to debug. 2013-12-04 13:53:36.582 wkhtmltopdf[27410:507] CoreText performance note: Client called CTFontCreateWithName() using name "Arial" and got font with PostScript name "ArialMT". For best performance, only use PostScript names when calling this API. 2013-12-04 13:53:36.584 wkhtmltopdf[27410:507] CoreText performance note: Client called CTFontCreateWithName() using name "Arial" and got font with PostScript name "ArialMT". For best performance, only use PostScript names when calling this API. ^C RuntimeError - command failed: /usr/local/bin/wkhtmltopdf --page-size Legal --print-media-type --quiet - -: pdfkit (0.5.4) lib/pdfkit/pdfkit.rb:73:in `to_pdf' pdfkit (0.5.4) lib/pdfkit/middleware.rb:21:in `call' warden (1.2.3) lib/warden/manager.rb:35:in `block in call' warden (1.2.3) lib/warden/manager.rb:34:in `catch' warden (1.2.3) lib/warden/manager.rb:34:in `call' rack (1.5.2) lib/rack/etag.rb:23:in `call' rack (1.5.2) lib/rack/conditionalget.rb:25:in `call' rack (1.5.2) lib/rack/head.rb:11:in `call' actionpack (4.0.0) lib/action_dispatch/middleware/params_parser.rb:27:in `call' actionpack (4.0.0) lib/action_dispatch/middleware/flash.rb:241:in `call' rack (1.5.2) lib/rack/session/abstract/id.rb:225:in `context' rack (1.5.2) lib/rack/session/abstract/id.rb:220:in `call' actionpack (4.0.0) lib/action_dispatch/middleware/cookies.rb:486:in `call' activerecord (4.0.0) lib/active_record/query_cache.rb:36:in `call' activerecord (4.0.0) lib/active_record/connection_adapters/abstract/connection_pool.rb:626:in `call' activerecord (4.0.0) lib/active_record/migration.rb:369:in `call' actionpack (4.0.0) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call' activesupport (4.0.0) lib/active_support/callbacks.rb:373:in `_run__4124003592524659480__call__callbacks' activesupport (4.0.0) lib/active_support/callbacks.rb:80:in `run_callbacks' actionpack (4.0.0) lib/action_dispatch/middleware/callbacks.rb:27:in `call' actionpack (4.0.0) lib/action_dispatch/middleware/reloader.rb:64:in `call' actionpack (4.0.0) lib/action_dispatch/middleware/remote_ip.rb:76:in `call' better_errors (1.0.1) lib/better_errors/middleware.rb:84:in `protected_app_call' better_errors (1.0.1) lib/better_errors/middleware.rb:79:in `better_errors_call' better_errors (1.0.1) lib/better_errors/middleware.rb:56:in `call' actionpack (4.0.0) lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call' actionpack (4.0.0) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call' railties (4.0.0) lib/rails/rack/logger.rb:38:in `call_app' railties (4.0.0) lib/rails/rack/logger.rb:21:in `block in call' activesupport (4.0.0) lib/active_support/tagged_logging.rb:67:in `block in tagged' activesupport (4.0.0) lib/active_support/tagged_logging.rb:25:in `tagged' activesupport (4.0.0) lib/active_support/tagged_logging.rb:67:in `tagged' railties (4.0.0) lib/rails/rack/logger.rb:21:in `call' actionpack (4.0.0) lib/action_dispatch/middleware/request_id.rb:21:in `call' rack (1.5.2) lib/rack/methodoverride.rb:21:in `call' rack (1.5.2) lib/rack/runtime.rb:17:in `call' activesupport (4.0.0) lib/active_support/cache/strategy/local_cache.rb:83:in `call' rack (1.5.2) lib/rack/lock.rb:17:in `call' actionpack (4.0.0) lib/action_dispatch/middleware/static.rb:64:in `call' railties (4.0.0) lib/rails/engine.rb:511:in `call' railties (4.0.0) lib/rails/application.rb:97:in `call' rack (1.5.2) lib/rack/content_length.rb:14:in `call' thin (1.6.0) lib/thin/connection.rb:82:in `block in pre_process' thin (1.6.0) lib/thin/connection.rb:80:in `catch' thin (1.6.0) lib/thin/connection.rb:80:in `pre_process' thin (1.6.0) lib/thin/connection.rb:55:in `process' thin (1.6.0) lib/thin/connection.rb:41:in `receive_data' eventmachine (1.0.3) lib/eventmachine.rb:187:in `run_machine' eventmachine (1.0.3) lib/eventmachine.rb:187:in `run' thin (1.6.0) lib/thin/backends/base.rb:73:in `start' thin (1.6.0) lib/thin/server.rb:162:in `start' rack (1.5.2) lib/rack/handler/thin.rb:16:in `run' rack (1.5.2) lib/rack/server.rb:264:in `start' railties (4.0.0) lib/rails/commands/server.rb:84:in `start' railties (4.0.0) lib/rails/commands.rb:78:in `block in ' railties (4.0.0) lib/rails/commands.rb:73:in `tap' railties (4.0.0) lib/rails/commands.rb:73:in `' bin/rails:4:in `require' bin/rails:4:in `'
这是一个臭名昭着的问题，你正在遇到它，因为你的HTML中可能有相对链接的资产（即图像，CSS，JS，字体等），而你的网络服务器只能处理一个请求/线程一时间（如WEBrick ）。
那会发生什么？ 当您请求其URL时，服务器开始生成PDF。 PDFkit查找链接的资产，因此它尝试从服务器加载此资产，该服务器恰好与运行PDFkit的服务器相同。 但是，服务器的单线程已经忙于运行PDFkit，因此它无法“释放”来提供所请求的资产。 总而言之，这是一个僵局–PDFkit正在等待等待PDFkit完成处理的同一台服务器上的资产，以便它可以将资产提供给PDFkit ……
解决方案 ： Base64将您的资产嵌入HTML中，以便PDFkit不需要发出任何其他请求（我个人喜欢的解决方案），或者暂时将资产卸载到另一台服务器（例如临时AWS桶）。 您也可以尝试使用启用了multithreading的unicorn或Thin Web服务器，或者添加config.threadsafe! 在in application.rb ，但不保证这些方法可行。
当然，这些hacks（嵌入资源或托管其他地方）应该只在开发环境中使用 – 你不应该在生产中遇到这些问题，因为实时服务器应该（希望）能够处理多个GET要求。
您可以在开发中使用unicorn ，一次提供多个请求。 并且易于设置。 参考http://dave.is/unicorn.html和https://devcenter.heroku.com/articles/rails-unicorn
它解决了我在开发中的问题。
这是一个workround助手
阿曼的回答帮了我很多忙。 这是我想出的一个实现。
module PdfHelper def pdf_image_tag(image_name) if Rails.env.development? || Rails.env.test? # Unless running a web server that can process 2 requests at the same # time, trying to insert an image in a PDF creates a deadlock: the server # can't finish processing the PDF request until it gets the image, but it # can't start processing the image request until it has finished # processing the PDF request. # This will not be a problem in production, but in dev, a workaround is # to base64 the image and insert its contents into the HTML image_data = Rails.application.assets[image_name].to_s image_tag "data:image/png;base64,#{::Base64.encode64(image_data)}" else image_tag image_name end end end
您收到此错误是因为默认情况下WEBrick是一个单线程服务器，并且能够一次完成一个请求（因为单个工作线程）。要在Rails 4.0中使WEBrick完全multithreading，只需将其添加到config/initializers/multithreaded_webrick.rb ：
# Remove Rack::Lock so WEBrick can be fully multi-threaded. require 'rails/commands/server' class Rails::Server def middleware middlewares = [] middlewares << [Rails::Rack::Debugger] if options[:debugger] middlewares << [::Rack::ContentLength] Hash.new middlewares end end
在你的application.rb中添加config.middleware.delete 'Rack::Lock'