1 USING: calendar help.markup help.syntax quotations ;
5 { $class-description "The class of mutual exclusion locks." } ;
8 { $values { "lock" lock } }
9 { $description "Creates a non-reentrant lock." } ;
11 HELP: <reentrant-lock>
12 { $values { "lock" lock } }
13 { $description "Creates a reentrant lock." } ;
15 HELP: with-lock-timeout
16 { $values { "lock" lock } { "timeout" { $maybe duration } } { "quot" quotation } }
17 { $description "Calls the quotation, ensuring that only one thread executes with the lock held at a time. If another thread is holding the lock, blocks until the thread releases the lock." }
18 { $errors "Throws an error if the lock could not be acquired before the timeout expires. A timeout value of " { $link f } " means the thread is willing to wait indefinitely." } ;
21 { $values { "lock" lock } { "quot" quotation } }
22 { $description "Calls the quotation, ensuring that only one thread executes with the lock held at a time. If another thread is holding the lock, blocks until the thread releases the lock." } ;
24 ARTICLE: "concurrency.locks.mutex" "Mutual-exclusion locks"
25 "A mutual-exclusion lock ensures that only one thread executes with the lock held at a time. They are used to protect critical sections so that certain operations appear to be atomic to other threads."
27 "There are two varieties of locks: non-reentrant and reentrant. The latter may be acquired recursively by the same thread. Attempting to do so with the former will deadlock."
37 { $class-description "The class of reader/writer locks." } ;
39 HELP: with-read-lock-timeout
40 { $values { "lock" lock } { "timeout" { $maybe duration } } { "quot" quotation } }
41 { $description "Calls the quotation, ensuring that no other thread is holding a write lock at the same time. If another thread is holding a write lock, blocks until the thread releases the lock." }
42 { $errors "Throws an error if the lock could not be acquired before the timeout expires. A timeout value of " { $link f } " means the thread is willing to wait indefinitely." } ;
45 { $values { "lock" lock } { "quot" quotation } }
46 { $description "Calls the quotation, ensuring that no other thread is holding a write lock at the same time. If another thread is holding a write lock, blocks until the thread releases the lock." } ;
48 HELP: with-write-lock-timeout
49 { $values { "lock" lock } { "timeout" { $maybe duration } } { "quot" quotation } }
50 { $description "Calls the quotation, ensuring that no other thread is holding a read or write lock at the same time. If another thread is holding a read or write lock, blocks until the thread releases the lock." }
51 { $errors "Throws an error if the lock could not be acquired before the timeout expires. A timeout value of " { $link f } " means the thread is willing to wait indefinitely." } ;
54 { $values { "lock" lock } { "quot" quotation } }
55 { $description "Calls the quotation, ensuring that no other thread is holding a read or write lock at the same time. If another thread is holding a read or write lock, blocks until the thread releases the lock." } ;
57 ARTICLE: "concurrency.locks.rw" "Read-write locks"
58 "A read-write lock encapsulates a common pattern in the implementation of concurrent data structures, where one wishes to ensure that a thread is able to see a consistent view of the structure for a period of time, during which no other thread modifies the structure."
60 "While this can be achieved with a simple " { $link "concurrency.locks.mutex" } ", performance will suffer, since in fact multiple threads can view the structure at the same time; serialization must only be enforced for writes."
62 "Read/write locks allow any number of threads to hold the read lock simultaneously, however attempting to acquire a write lock blocks until all other threads release read locks and write locks."
64 "Read/write locks are reentrant. A thread holding a write lock may acquire a read lock or a write lock without blocking. However a thread holding a read lock may not acquire a write lock recursively since that could break invariants assumed by the code executing with the read lock held."
71 "Versions of the above that take a timeout duration:"
73 with-read-lock-timeout
74 with-write-lock-timeout
77 ARTICLE: "concurrency.locks" "Locks"
78 "A " { $emphasis "lock" } " is an object protecting a critical region of code, enforcing a particular mutual-exclusion policy. The " { $vocab-link "concurrency.locks" } " vocabulary implements two types of locks:"
80 "concurrency.locks.mutex"
81 "concurrency.locks.rw"
84 ABOUT: "concurrency.locks"