diff options
Diffstat (limited to 'libjava/interpret-run.cc')
| -rw-r--r-- | libjava/interpret-run.cc | 24 |
1 files changed, 18 insertions, 6 deletions
diff --git a/libjava/interpret-run.cc b/libjava/interpret-run.cc index f858c97..2934b9b 100644 --- a/libjava/interpret-run.cc +++ b/libjava/interpret-run.cc @@ -382,12 +382,24 @@ details. */ #else // !DEBUG #undef NEXT_INSN #define NEXT_INSN goto *((pc++)->insn) -#define REWRITE_INSN(INSN,SLOT,VALUE) \ - do { \ - pc[-2].insn = INSN; \ - pc[-1].SLOT = VALUE; \ - } \ - while (0) + +// REWRITE_INSN does nothing. +// +// Rewriting a multi-word instruction in the presence of multiple +// threads leads to a data race if a thread reads part of an +// instruction while some other thread is rewriting that instruction. +// For example, an invokespecial instruction may be rewritten to +// invokespecial_resolved and its operand changed from an index to a +// pointer while another thread is executing invokespecial. This +// other thread then reads the pointer that is now the operand of +// invokespecial_resolved and tries to use it as an index. +// +// Fixing this requires either spinlocks, a more elaborate data +// structure, or even per-thread allocated pages. It's clear from the +// locking in meth->compile below that the presence of multiple +// threads was contemplated when this code was written, but the full +// consequences were not fully appreciated. +#define REWRITE_INSN(INSN,SLOT,VALUE) #undef INTERP_REPORT_EXCEPTION #define INTERP_REPORT_EXCEPTION(Jthrowable) /* not needed when not debugging */ |