Typos and a bad hyperlink in "The Foreign Function and Memory API " tutorial ( https://dev.java/learn/ffm/ )

[willy-b]

Hello dev.java team!

Thanks again for all the excellent content. I am filing a ticket to report some typos and a broken link that I found while reviewing the "The Foreign Function and Memory API " tutorial ( https://dev.java/learn/ffm/ ) in case the team is interested to fix these items.

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In the latest version of https://dev.java/learn/ffm/upcall/ (archived as is at https://web.archive.org/web/20260712004940/https://dev.java/learn/ffm/upcall/ )

• In the sentence

  nbemb represents the number of elements in the array,

  "nbemb" should be "nmemb" (to be consistent with the code sample above it and make sense as "number of members")

• In the sentence

  Let's start with how to represent in Java the method that compares two elements, in this case two int values::

  "values::" should be "values:"

• In the sentence

  The Linker.upcallStub(MethodHandle,FunctionDescriptor,Arena,Linker.Option...) method needs three arguments:

  "Linker.upcallStub(MethodHandle,FunctionDescriptor,Arena,Linker.Option...)" link has the wrong fragment for the method causing it not to scroll to the intended method on the javadoc page, linking to https://docs.oracle.com/en/java/javase/26/docs/api/java.base/java/lang/foreign/Linker.html#upcallStub(java.lang.invoke.MethodHandle,java.lang.foreign.FunctionDescriptor,java.lang.foreign.MemorySession) ,
  when, to be consistent with the link text and the actual method available, it should link to https://docs.oracle.com/en/java/javase/26/docs/api/java.base/java/lang/foreign/Linker.html#upcallStub(java.lang.invoke.MethodHandle,java.lang.foreign.FunctionDescriptor,java.lang.foreign.Arena,java.lang.foreign.Linker.Option...) .

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In the latest version of https://dev.java/learn/ffm/troubleshoot/ (archived as is at https://web.archive.org/web/20260712045513/https://dev.java/learn/ffm/troubleshoot/ ) ,

• In the code snippet

  // Convert errno code to a string message:
             String errrorString = ((MemorySegment) strerror.invokeExact(errno))
                     .reinterpret(Long.MAX_VALUE).getString(0);
             IO.println("errno string: " + errrorString);
  

  "errrorString" should be "errorString" (3 'r's should be 2 'r's). (in two places in the code)

• The Method Restriction reason table methods are not hyperlinked to their javadocs, which is inconsistent with elsewhere in these tutorials (and less useful than if hyperlinked)

• In the Method Restriction reason table, it may be useful to double check the two columns for a single row

  Linker.upcallStub(MethodHandle, FunctionDescriptor, Arena, Linker.Option...)
  When you create downcall handles, the linker can't check whether the function pointer you are creating is the correct one for the for the downcall you are passing it to.

It seems the above may be potentially mismatched as the method is "Linker.upcallStub" but the description is explaining why downcall handles are restricted.

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In the latest version of https://dev.java/learn/ffm/access-memory/ (archived as is at https://web.archive.org/web/20260711215115/https://dev.java/learn/ffm/access-memory/ )

• In the sentence

  A global arena (Arena.global()) has as main trait: any thread can access memory segments allocated with this arena.

  "has as main trait:" is ungrammatical. Maybe this was intended to be "has a main trait:"?

  Also should it be "The global arena" instead of "A global arena"? In the Java documentation,
  they consistently use "The global arena", e.g. at https://docs.oracle.com/en/java/javase/26/docs/api/java.base/java/lang/foreign/Arena.html

  The simplest arena is the global arena. The global arena features an unbounded lifetime. The scope of the global arena is the global scope.

  or at the Javadoc for https://docs.oracle.com/en/java/javase/26/docs/api/java.base/java/lang/foreign/Arena.html#global() :

  Returns the global arena.

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In the latest version of https://dev.java/learn/ffm/jextract/ (archived as is at https://web.archive.org/web/20260712045824/https://dev.java/learn/ffm/jextract/ )

• In the sentence

  Some libraries are incredibly large (such as Windows.h), and you might not be need all the jextract generated code.

  "you might not be need all the" should be "you might not need all the" (remove "be").

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In the latest version of https://dev.java/learn/ffm/access-structure/ (archived as is at https://web.archive.org/web/20260711043546/https://dev.java/learn/ffm/access-structure/ )

• In the sentence

  An elegant solution is to use memory layouts that are more efficiently to initialize and can access more complex native data types such as C structures.

  "that are more efficiently to initialize" should be "that are more efficient to initialize".

• In the sentence

  You can check the result of your work by pasting the above snippet in a jshell session and obtain:

  "obtain" should be "obtaining"..

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Thanks very much!

[JosePaumard]

Thank you again for your report! A fix is on its way.
As for your report on downcall handle creation, I forwarded it to the author of the page, so the fix is still under way. Again, thank you!

[willy-b]

The changes mentioned in your last comment haven't posted yet in:

• https://dev.java/learn/ffm/upcall/ as of https://web.archive.org/web/20260713030359/https://dev.java/learn/ffm/upcall/?nonce=1
• https://dev.java/learn/ffm/troubleshoot/ as of https://web.archive.org/web/20260713013602/https://dev.java/learn/ffm/troubleshoot/?nonce=1
• https://dev.java/learn/ffm/access-memory/ as of https://web.archive.org/web/20260713030759/https://dev.java/learn/ffm/access-memory/?nonce=1
• https://dev.java/learn/ffm/jextract/ as of https://web.archive.org/web/20260713030503/https://dev.java/learn/ffm/jextract/?nonce=1
• https://dev.java/learn/ffm/access-structure/ as of https://web.archive.org/web/20260713030852/https://dev.java/learn/ffm/access-structure/?nonce=1

In the meantime I can report one additional typo I found from the article author:

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In the latest version of https://dev.java/learn/ffm/troubleshoot/ (archived as is at https://web.archive.org/web/20260713013602/https://dev.java/learn/ffm/troubleshoot/?nonce=1 )

• In the sentence

  The method enables native access for the specified module if the caller's module has native acces.

  "acces" should be "access".

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Thanks very much!

[JosePaumard]

Thank you again for your report! A fix is on its way.

[ammbra]

I fixed the rest related to this issue 😁