One important fact to know about static constructors is that they effectively execute under a lock. The CLR must ensure that each type is initialized exactly once, and so it uses locking to prevent multiple threads from executing the same static constructor. A caveat, however, is that executing the static constructor under a lock opens up the possibility of deadlocks. <\/p>\n
This example demonstrates the deadlock:<\/p>\n
using System.Threading;<\/span> static MyClass()<\/span> In the example above, the static constructor waits for the helper thread to complete. The thread executing the static constructor holds some CLR-internal lock. Then, if the CLR needs to acquire the CLR-internal lock in order to execute the helper thread – and that seems to be exactly what happens – a deadlock will occur.<\/p>\n This CLR behavior is defined in section 10.5.3.3 of the ECMA CLI specification:<\/p>\n “Type initialization alone shall not create a deadlock unless some code called from a type initializer (directly or indirectly) explicitly invokes blocking operations.”<\/p>\n So, any operation that blocks the current thread in a static constructor potentially risks a deadlock. For example, just as waiting on threads can deadlock a static constructor, waiting on a task can have the same effect. And the same goes for Parallel.For<\/strong>, Parallel.ForEach<\/strong>, Parallel.Invoke<\/strong>, PLINQ queries<\/strong>, etc.<\/p>\n This example uses Parallel.For and also deadlocks:<\/p>\n using System.Threading.Tasks;<\/span> static int s_value = ComputeValue();<\/span><\/p>\n private static int ComputeValue()<\/span> As this example shows, Parallel.For called from a static constructor can also cause a deadlock. Also, notice that in the example above, the Parallel.For is actually called from a static initializer, not a static constructor. For all intents and purposes, static initializers execute as a part of the static constructor, and so they are also at risk of the same kind of deadlock.<\/p>\n So, to avoid the risk of deadlocks, avoid blocking the current thread in static constructors and initializers: don’t wait on tasks, threads, wait handles or events, don’t acquire locks, and don’t execute blocking parallel operations like parallel loops, Parallel.Invoke and PLINQ queries.<\/p><\/p>\n","protected":false},"excerpt":{"rendered":" One important fact to know about static constructors is that they effectively execute under a lock. The CLR must ensure that each type is initialized exactly once, and so it uses locking to prevent multiple threads from executing the same static constructor. A caveat, however, is that executing the static constructor under a lock opens up the possibility of […]<\/p>\n","protected":false},"author":481,"featured_media":58792,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[7908],"tags":[],"class_list":["post-56053","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-pfxteam"],"acf":[],"blog_post_summary":" One important fact to know about static constructors is that they effectively execute under a lock. The CLR must ensure that each type is initialized exactly once, and so it uses locking to prevent multiple threads from executing the same static constructor. A caveat, however, is that executing the static constructor under a lock opens up the possibility of […]<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/dotnet\/wp-json\/wp\/v2\/posts\/56053","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/dotnet\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/dotnet\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/dotnet\/wp-json\/wp\/v2\/users\/481"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/dotnet\/wp-json\/wp\/v2\/comments?post=56053"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/dotnet\/wp-json\/wp\/v2\/posts\/56053\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/dotnet\/wp-json\/wp\/v2\/media\/58792"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/dotnet\/wp-json\/wp\/v2\/media?parent=56053"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/dotnet\/wp-json\/wp\/v2\/categories?post=56053"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/dotnet\/wp-json\/wp\/v2\/tags?post=56053"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
class MyClass<\/span>
{<\/span>
static void Main() { \/* Won’t run… the static constructor deadlocks *\/ }<\/span><\/p>\n
{<\/span>
Thread thread = new Thread(arg => { });<\/span>
thread.Start();<\/span>
thread.Join();<\/span>
}<\/span>
}<\/span><\/p>\n
class MyClass<\/span>
{<\/span>
static void Main() { \/* Won’t run… the static constructor deadlocks *\/ }<\/span><\/p>\n
{<\/span>
Action emptyAction = () => {};
Parallel.Invoke(emptyAction, emptyAction);
<\/span> return 42;<\/span>
}<\/span>
}<\/span><\/p>\n