Bug 5537 – invariant._d_invariant() failing in std.concurrency.MessageBox.get

This program currently results in a segfault: import std.concurrency; import std.stdio; void main() { int currThreads = 0; enum maxThreads = 6; size_t totalThreads = 0; auto recProc = (Tid tid) { writeln(++totalThreads); }; for(size_t i = 0; i < 1_000; ++i) { if(currThreads < maxThreads) receiveTimeout(1, recProc); else receive(recProc); spawn(&threadFunc, thisTid); } while(currThreads > 0) receive(recProc); } void threadFunc(Tid parentTid) { send(parentTid, thisTid); } This is using the latest versions of druntime and phobos from git. The stack trace I get with gdb is #0 0x080ade03 in invariant._d_invariant() () #1 0x080a56cc in std.concurrency.MessageBox.get!(long,void delegate(Tid tid)).get (this=0x0, _param_1=579319349254397504, _param_0=10000) at /home/jmdavis/dmd2/linux/bin/../../src/phobos/std/concurrency.d:716 #2 0x080a56aa in std.concurrency.receiveTimeout!(void delegate(Tid tid)).receiveTimeout (_param_1=579319349254397504, ms=1) at /home/jmdavis/dmd2/linux/bin/../../src/phobos/std/concurrency.d:501 #3 0x080a27a5 in D main () at l.d:18 #4 0x080add86 in rt.dmain2.main() () #5 0x080add18 in rt.dmain2.main() () #6 0x080addca in rt.dmain2.main() () #7 0x080add18 in rt.dmain2.main() () #8 0x080adcc4 in main () If I simplify the program that it uses only receive and not receiveTimeout, it still fails, so it's not an issue specific to receiveTimeout. I have also confirmed that the check-in 94bd4f661be79db34faedf76ca139115a07a9dd3 (Issue 4307 - spawn()'ed thread doesn't terminate) didn't cause the problem. I have no idea what invariant._d_invariant() is - std.concurrency doesn't have any invariants in it - but this bug makes spawn utterly useless.

Using git-bisect, I have confirmed that it is this commit to Phobos which broke it: https://github.com/D-Programming-Language/phobos/commit/ecc7390670a122dec11183cbefbef2e7d9477921

This no longer segfaults, so I assume that the issue has been fixed.